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/api/play_profiles.ts

@@ -0,0 +1,35 @@
+import { api } from './client'
+import type { PlayProfile } from '../types'
+
+// Payload accepted by create / update.
+export interface PlayProfileInput {
+  user_id?: string
+  name: string
+  is_default: boolean
+  content_rating_limit?: string
+  allow_adult: boolean
+  require_pin: boolean
+  pin?: string
+  preferred_subtitle_lang?: string
+  preferred_audio_lang?: string
+  autoplay_next: boolean
+  skip_intro: boolean
+  allowed_library_ids: string[]
+}
+
+// playProfilesAPI wraps /play-profiles. The admin variant adds ?all=true.
+export const playProfilesAPI = {
+  list: (all = false) =>
+    api
+      .get<PlayProfile[]>('/play-profiles', { params: all ? { all: 'true' } : {} })
+      .then((r) => r.data),
+
+  create: (input: PlayProfileInput) =>
+    api.post<PlayProfile>('/play-profiles', input).then((r) => r.data),
+
+  update: (id: string, input: PlayProfileInput) =>
+    api.put<PlayProfile>(`/play-profiles/${id}`, input).then((r) => r.data),
+
+  remove: (id: string) =>
+    api.delete(`/play-profiles/${id}`).then((r) => r.data),
+}