feat: port remaining Vue UI surfaces with full backend support

Backend additions:
- New GORM models: NotifyChannel, PlayProfile (with PIN hashing).
- NotifyChannelService: multi-channel CRUD + unified dispatcher
  supporting Telegram / Bark / WeChat / Webhook with optional
  per-channel event filtering.
- PlayProfileService: per-user 'viewing personas' with
  content-rating gates, library scoping, PIN protection, and
  player defaults (autoplay, skip-intro, audio/subtitle prefs).
- New endpoints:
    GET    /admin/notify/channels           list
    POST   /admin/notify/channels           create
    PUT    /admin/notify/channels/:id       update
    DELETE /admin/notify/channels/:id       delete
    POST   /admin/notify/channels/:id/test  send test
    GET    /play-profiles                   list (admin: ?all=true)
    POST   /play-profiles                   create
    PUT    /play-profiles/:id               update
    DELETE /play-profiles/:id               delete
    GET    /media/recent                    home page rail
    GET    /media/stats                     library composition
    GET    /watch-history                   list
    GET    /watch-history/stats             aggregate
    GET    /watch-history/continue          continue-watching rail
    DELETE /watch-history[?media_id=]       clear
    DELETE /watch-history/:id               remove one
    GET    /discover/sections               available rails
    GET    /discover/feed?sections=a,b      multi-section TMDb fetch
    GET    /system/info                     name/version/runtime
    GET    /system/status                   uptime/cpu/mem/disk
    GET    /system/scheduler                read-only scheduler view
    GET    /stats/overview                  counts only
    GET    /stats/trend                     daily plays
    GET    /stats/top-content               most played
    GET    /stats/libraries                 per-library size
    GET    /stats/monitor                   live hardware

Frontend additions:
- New API helpers: notify_channels, play_profiles, history,
  stats_extra, media_extra, discover_extra, system.
- ProfileManagementPage (/play-profiles): full CRUD form with
  PIN management, library scoping, language preferences.
- NotifyChannelsPage (/notify-channels, admin): typed config
  forms per channel type + per-channel test action.
- SettingsPage (/settings, admin): grouped key/value editor
  covering General, Organize/Scrape, Adult, qBittorrent.
- Layout sidebar links and App.tsx routes wired for all three.

web/src/App.tsx

@@ -84,6 +84,15 @@ const StrmPage = lazy(() =>
 const ToolsPage = lazy(() =>
   import('./pages/ToolsPage').then((m) => ({ default: m.ToolsPage })),
 )
+const ProfileManagementPage = lazy(() =>
+  import('./pages/ProfileManagementPage').then((m) => ({ default: m.ProfileManagementPage })),
+)
+const NotifyChannelsPage = lazy(() =>
+  import('./pages/NotifyChannelsPage').then((m) => ({ default: m.NotifyChannelsPage })),
+)
+const SettingsPage = lazy(() =>
+  import('./pages/SettingsPage').then((m) => ({ default: m.SettingsPage })),
+)
 
 const Loading = () => <p className="px-6 py-8 text-slate-500">加载中…</p>
 
@@ -118,6 +127,7 @@ export default function App() {
           <Route path="sites" element={<SitesPage />} />
           <Route path="site-search" element={<SiteSearchPage />} />
           <Route path="ai" element={<AIAssistantPage />} />
+          <Route path="play-profiles" element={<ProfileManagementPage />} />
           <Route
             path="files"
             element={
@@ -190,6 +200,22 @@ export default function App() {
               </RequireAdmin>
             }
           />
+          <Route
+            path="notify-channels"
+            element={
+              <RequireAdmin>
+                <NotifyChannelsPage />
+              </RequireAdmin>
+            }
+          />
+          <Route
+            path="settings"
+            element={
+              <RequireAdmin>
+                <SettingsPage />
+              </RequireAdmin>
+            }
+          />
           <Route
             path="stats"
             element={