feat(config): add floating save button (FAB) for issue #266 (#400)

* docs: add floating save button design spec for issue #266

* docs: add implementation plan for floating save button

* feat(config): add floating save button (FAB) for issue #266

docs/superpowers/plans/001-floating-save-button.md

@@ -0,0 +1,132 @@
+# Floating Save Button Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add a floating save button (FAB) to the config page that appears when configuration changes are detected.
+
+**Architecture:** Inline FAB implementation using framer-motion AnimatePresence for enter/exit animations. Fixed-position circular button with slide-up animation, reusing existing hasChanges state and handleSave function.
+
+**Tech Stack:** React, framer-motion (v11.18.2), shadcn-bridge/heroui Button, Tailwind CSS
+
+---
+
+## File Structure
+
+| File | Action | Purpose |
+|------|--------|---------|
+| `vite-frontend/src/pages/config.tsx` | Modify | Add FAB imports and component at page bottom |
+
+---
+
+### Task 1: Add framer-motion Imports
+
+**Files:**
+- Modify: `vite-frontend/src/pages/config.tsx:1-5`
+
+- [ ] **Step 1: Add AnimatePresence and motion imports**
+
+Add import statement after existing framer-motion imports (or at top if none exist).
+
+Current imports at line 1-2:
+```typescript
+import { useState, useEffect, useRef } from "react";
+import { useNavigate } from "react-router-dom";
+```
+
+Add new import after line 2:
+```typescript
+import { AnimatePresence, motion } from "framer-motion";
+```
+
+- [ ] **Step 2: Commit import addition**
+
+```bash
+git add vite-frontend/src/pages/config.tsx
+git commit -m "feat(config): add framer-motion imports for FAB animation"
+```
+
+---
+
+### Task 2: Add FAB Component
+
+**Files:**
+- Modify: `vite-frontend/src/pages/config.tsx:1220-1224` (end of component)
+
+- [ ] **Step 1: Add FAB at end of component (before closing div)**
+
+Locate the end of `ConfigPage` component (line ~1223, the closing `</div>` after all modals).
+
+Insert FAB component before the closing `</div>`:
+
+```tsx
+      {/* Floating Save Button (FAB) */}
+      <AnimatePresence>
+        {hasChanges && (
+          <motion.div
+            initial={{ y: 100, opacity: 0 }}
+            animate={{ y: 0, opacity: 1 }}
+            exit={{ y: 100, opacity: 0 }}
+            transition={{ type: "spring", damping: 20, stiffness: 300 }}
+            className="fixed bottom-6 right-6 z-50"
+          >
+            <Button
+              isIconOnly
+              color="primary"
+              size="lg"
+              className="w-12 h-12 rounded-full shadow-lg"
+              isLoading={saving}
+              onPress={handleSave}
+            >
+              {!saving && <SaveIcon className="w-5 h-5" />}
+            </Button>
+          </motion.div>
+        )}
+      </AnimatePresence>
+    </div>
+  );
+}
+```
+
+- [ ] **Step 2: Run dev server to verify**
+
+```bash
+cd vite-frontend && npm run dev
+```
+
+Manual verification checklist:
+- Open config page at http://localhost:3000/config
+- Modify any config field
+- Verify FAB appears with slide-up animation
+- Click FAB to save
+- Verify FAB disappears with slide-down animation after save
+- Scroll page and verify FAB stays fixed in viewport corner
+- Test on mobile viewport (resize browser or use dev tools)
+
+- [ ] **Step 3: Commit FAB implementation**
+
+```bash
+git add vite-frontend/src/pages/config.tsx
+git commit -m "feat(config): add floating save button (FAB) for issue #266"
+```
+
+---
+
+## Verification Summary
+
+| Requirement | Verification Method |
+|-------------|---------------------|
+| FAB hidden by default | Visual: no FAB on page load with no changes |
+| FAB appears on change | Visual: modify field → FAB slides up |
+| Fixed position | Visual: scroll page → FAB stays in corner |
+| Slide-up animation | Visual: observe animation timing/bounce |
+| Slide-down on save | Visual: click save → FAB slides down |
+| Loading state | Visual: click save → spinner shown during save |
+| Mobile compatibility | Visual: resize to mobile viewport → same behavior |
+
+---
+
+## Self-Review Checklist
+
+- [x] Spec coverage: All requirements from design doc covered (imports + FAB component, animation params, button style, interaction behavior)
+- [x] No placeholders: All code shown, no TBD/TODO
+- [x] Type consistency: SaveIcon (line 45-59), handleSave (line 372-434), hasChanges (line 214), saving (line 213) all exist in config.tsx

docs/superpowers/specs/2026-04-01-floating-save-button-design.md

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+# Floating Save Button Design
+
+**Date:** 2026-04-01
+**Issue:** https://github.com/Sagit-chu/flvx/issues/266
+**Status:** Approved
+
+## Overview
+
+Add a Floating Action Button (FAB) to the config page (`vite-frontend/src/pages/config.tsx`) that appears when configuration changes are detected, allowing users to save without scrolling to the top.
+
+## Requirements
+
+From Issue #266:
+
+1. **Default hidden**: FAB not visible when no config changes
+2. **Show on change**: Auto-display when `hasChanges` becomes true
+3. **Fixed position**: Suspended at bottom-right corner, does not scroll with page
+4. **Mobile compatible**: Same behavior on desktop and mobile devices
+
+## Design Decisions
+
+### 1. Implementation Approach
+
+**Inline FAB in config.tsx** (not a reusable component)
+
+- Rationale: Current need is limited to config page only
+- State management (`hasChanges`, `saving`) already exists in the page
+- framer-motion patterns already established in project
+- Avoids over-abstraction (YAGNI)
+
+### 2. UI Structure
+
+Position: `fixed bottom-6 right-6` (24px from viewport edges)
+
+Visual layout:
+```
+┌──────────────────────────────────────┐
+│  [页面内容，可滚动]                    │
+│                                      │
+│                                [●]   │ ← FAB (fixed position)
+└──────────────────────────────────────┘
+```
+
+### 3. Button Appearance
+
+- Shape: Circular (`w-12 h-12 rounded-full`)
+- Color: Primary (matches existing save button)
+- Icon: SaveIcon (already defined in config.tsx)
+- Shadow: `shadow-lg` for visual hierarchy
+- Style: Icon-only (no text label)
+
+### 4. Animation
+
+Using framer-motion with `AnimatePresence`:
+
+| Phase | Properties |
+|-------|------------|
+| `initial` | `{ y: 100, opacity: 0 }` - starts below viewport |
+| `animate` | `{ y: 0, opacity: 1 }` - slides up to position |
+| `exit` | `{ y: 100, opacity: 0 }` - slides back down on hide |
+
+Transition config:
+```typescript
+transition={{ type: "spring", damping: 20, stiffness: 300 }}
+```
+
+Spring parameters produce Material Design-like feel: smooth entrance, slight bounce settle.
+
+### 5. Interaction Details
+
+- **Click**: Calls existing `handleSave()` function
+- **Loading state**: Button shows Spinner when `saving === true`
+- **Hover**: Inherits Button component's primary color hover behavior
+- **z-index**: `z-50` (above page content, below modals)
+- **Prevent duplicate click**: Button disabled when `saving === true`
+
+## Technical Implementation
+
+### Code Location
+
+File: `vite-frontend/src/pages/config.tsx`
+
+### Required Imports
+
+```typescript
+import { AnimatePresence, motion } from "framer-motion";
+```
+
+### FAB Component Structure
+
+```tsx
+<AnimatePresence>
+  {hasChanges && (
+    <motion.div
+      initial={{ y: 100, opacity: 0 }}
+      animate={{ y: 0, opacity: 1 }}
+      exit={{ y: 100, opacity: 0 }}
+      transition={{ type: "spring", damping: 20, stiffness: 300 }}
+      className="fixed bottom-6 right-6 z-50"
+    >
+      <Button
+        isIconOnly
+        color="primary"
+        size="lg"
+        className="w-12 h-12 rounded-full shadow-lg"
+        isLoading={saving}
+        onPress={handleSave}
+      >
+        {!saving && <SaveIcon className="w-5 h-5" />}
+      </Button>
+    </motion.div>
+  )}
+</AnimatePresence>
+```
+
+### Placement
+
+Insert FAB at the end of the component, before the closing `</div>` (after all Cards and Modals).
+
+### Dependencies
+
+- framer-motion: Already installed (v11.18.2)
+- Button: Already imported from `@/shadcn-bridge/heroui/button`
+- SaveIcon: Already defined in config.tsx
+
+## Behavior Matrix
+
+| State | FAB Visibility | Button Enabled |
+|-------|----------------|----------------|
+| `hasChanges = false` | Hidden (not rendered) | N/A |
+| `hasChanges = true, saving = false` | Visible, animating in | Yes |
+| `hasChanges = true, saving = true` | Visible | No (loading) |
+| Save success | Hidden (animating out) | N/A |
+
+## Responsive Behavior
+
+No special handling needed. `fixed bottom-6 right-6` works identically on:
+- Desktop browsers
+- Mobile browsers
+- H5/WebView mode
+
+The FAB maintains consistent 24px margin from viewport edges regardless of screen size.
+
+## Edge Cases
+
+1. **Multiple rapid toggles**: AnimatePresence handles gracefully - exit animation completes before new enter animation
+2. **Page unload with unsaved changes**: Not addressed in this design (separate concern)
+3. **FAB covers existing warning banner**: z-50 places FAB above the warning banner at line 1004-1013
+
+## Testing Checklist
+
+After implementation, verify:
+
+- [ ] FAB appears when any config field is modified
+- [ ] FAB slides up from bottom on appearance
+- [ ] FAB slides down to bottom on disappearance
+- [ ] FAB fixed position during page scroll
+- [ ] FAB triggers save on click
+- [ ] FAB shows spinner during save
+- [ ] FAB disappears after successful save
+- [ ] FAB works on mobile viewport
+- [ ] FAB does not interfere with Modal dialogs

vite-frontend/src/pages/config.tsx

@@ -1,5 +1,6 @@
 import { useState, useEffect, useRef } from "react";
 import { useNavigate } from "react-router-dom";
+import { AnimatePresence, motion } from "framer-motion";
 import toast from "react-hot-toast";
 
 import { Button } from "@/shadcn-bridge/heroui/button";
@@ -1220,6 +1221,30 @@ export default function ConfigPage() {
           )}
         </ModalContent>
       </Modal>
+
+      {/* Floating Save Button (FAB) */}
+      <AnimatePresence>
+        {hasChanges && (
+          <motion.div
+            initial={{ y: 100, opacity: 0 }}
+            animate={{ y: 0, opacity: 1 }}
+            exit={{ y: 100, opacity: 0 }}
+            transition={{ type: "spring", damping: 20, stiffness: 300 }}
+            className="fixed bottom-6 right-6 z-50"
+          >
+            <Button
+              isIconOnly
+              color="primary"
+              size="lg"
+              className="w-12 h-12 rounded-full shadow-lg"
+              isLoading={saving}
+              onPress={handleSave}
+            >
+              {!saving && <SaveIcon className="w-5 h-5" />}
+            </Button>
+          </motion.div>
+        )}
+      </AnimatePresence>
     </div>
   );
 }