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.

internal/service/service.go

@@ -53,6 +53,8 @@ type Container struct {
 	Emby         *EmbyService
 	Backup       *BackupService
 	Notifier     *NotifierService
+	NotifyChannels *NotifyChannelService
+	PlayProfiles *PlayProfileService
 	Organizer    *OrganizerService
 	Douban       *DoubanProvider
 	Site         *SiteService
@@ -89,6 +91,8 @@ func New(cfg *config.Config, log *zap.Logger, repos *repository.Container) *Cont
 	emby := NewEmbyService(cfg, log, repos)
 	backup := NewBackupService(cfg, log, repos.DB)
 	notifier := NewNotifierService(log, repos)
+	notifyChannels := NewNotifyChannelService(log, repos)
+	playProfiles := NewPlayProfileService(log, repos)
 	organizer := NewOrganizerService(cfg, log, repos)
 	douban := NewDoubanProvider(cfg, log)
 	siteService := NewSiteService(log, repos)
@@ -134,6 +138,8 @@ func New(cfg *config.Config, log *zap.Logger, repos *repository.Container) *Cont
 		Emby:         emby,
 		Backup:       backup,
 		Notifier:     notifier,
+		NotifyChannels: notifyChannels,
+		PlayProfiles: playProfiles,
 		Organizer:    organizer,
 		Douban:       douban,
 		Site:         siteService,