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/model/model.go

@@ -229,6 +229,52 @@ type Site struct {
 	Downloader  string `gorm:"size:50" json:"downloader,omitempty"`
 }
 
+// NotifyChannel is one named outbound notification destination.
+//
+// The Config column holds a JSON blob whose schema depends on the
+// ChannelType (telegram/wechat/bark/webhook):
+//
+//	telegram → {bot_token, chat_id}
+//	wechat   → {sendkey}
+//	bark     → {device_key, server?}
+//	webhook  → {url, method, headers (JSON string), body_template}
+//
+// The Events column is a JSON array of event-type strings the channel
+// subscribes to; an empty array means "all events".
+type NotifyChannel struct {
+	Base
+	Name        string `gorm:"size:128;not null" json:"name"`
+	ChannelType string `gorm:"size:32;not null" json:"channel_type"`
+	Config      string `gorm:"type:text;not null" json:"config"`
+	Enabled     bool   `gorm:"default:true" json:"enabled"`
+	Events      string `gorm:"type:text;default:'[]'" json:"events"`
+}
+
+// PlayProfile lets one user define multiple "viewing personas" with
+// different content-rating limits, library access, and player defaults.
+// The original Vue project sketched this out as a forward-looking
+// feature; we materialise it server-side so the React port can fully
+// function without dropping the screen.
+//
+// AllowedLibraryIDs is a JSON array of library UUIDs (empty = all).
+type PlayProfile struct {
+	Base
+	UserID                string `gorm:"index;size:36;not null" json:"user_id"`
+	Name                  string `gorm:"size:64;not null" json:"name"`
+	IsDefault             bool   `gorm:"default:false" json:"is_default"`
+	ContentRatingLimit    string `gorm:"size:16" json:"content_rating_limit,omitempty"`
+	AllowAdult            bool   `gorm:"default:false" json:"allow_adult"`
+	RequirePIN            bool   `gorm:"default:false" json:"require_pin"`
+	PINHash               string `gorm:"size:128" json:"-"`
+	PreferredSubtitleLang string `gorm:"size:16" json:"preferred_subtitle_lang,omitempty"`
+	PreferredAudioLang    string `gorm:"size:16" json:"preferred_audio_lang,omitempty"`
+	AutoplayNext          bool   `gorm:"default:true" json:"autoplay_next"`
+	SkipIntro             bool   `gorm:"default:false" json:"skip_intro"`
+	AllowedLibraryIDs     string `gorm:"type:text;default:'[]'" json:"allowed_library_ids"`
+	TotalWatchTime        int64  `gorm:"default:0" json:"total_watch_time"`
+	LastActiveAt          *time.Time `json:"last_active_at,omitempty"`
+}
+
 // AllModels returns the slice consumed by gorm.AutoMigrate.
 func AllModels() []interface{} {
 	return []interface{}{
@@ -246,5 +292,7 @@ func AllModels() []interface{} {
 		&Site{},
 		&AccessLog{},
 		&APIConfig{},
+		&NotifyChannel{},
+		&PlayProfile{},
 	}
 }