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/handler/discover_extra.go

@@ -0,0 +1,79 @@
+// Package handler — multi-section discover endpoints.
+//
+// The Vue DiscoverView paginates a configurable list of "sections"
+// (trending day/week, popular movies, top rated, etc.) and asks the
+// backend for a feed keyed by section name. We mirror that surface so
+// the React DiscoverPage can render the same rails without a rewrite.
+package handler
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/ShukeBta/MediaStationGo/internal/service"
+)
+
+// discoverSectionsHandler returns the catalog of sections the UI can
+// pick from. The names match the upstream Vue UI so existing settings
+// keep working.
+func discoverSectionsHandler(_ *service.Container) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"sections": []gin.H{
+				{"key": "trending_day", "label": "今日热门"},
+				{"key": "trending_week", "label": "本周热门"},
+				{"key": "popular_movie", "label": "热门电影"},
+				{"key": "popular_tv", "label": "热门剧集"},
+				{"key": "top_rated_movie", "label": "高分电影"},
+				{"key": "upcoming_movie", "label": "即将上映"},
+			},
+		})
+	}
+}
+
+// discoverFeedHandler resolves one or more section keys (?sections=a,b)
+// to TMDb endpoint paths and returns the joined results keyed by
+// section name. Unknown keys are silently dropped so URL typos don't
+// break the page.
+func discoverFeedHandler(svc *service.Container) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		keys := strings.Split(c.DefaultQuery("sections", "trending_day,popular_movie"), ",")
+		out := gin.H{}
+		for _, raw := range keys {
+			k := strings.TrimSpace(raw)
+			path := sectionPath(k)
+			if path == "" {
+				continue
+			}
+			items, err := svc.Discover.Fetch(c.Request.Context(), path)
+			if err != nil {
+				svc.Log.Debug("discover fetch failed", )
+				items = nil
+			}
+			out[k] = items
+		}
+		c.JSON(http.StatusOK, out)
+	}
+}
+
+// sectionPath maps the UI-facing key to the TMDb endpoint suffix.
+func sectionPath(k string) string {
+	switch k {
+	case "trending_day":
+		return "/trending/movie/day"
+	case "trending_week":
+		return "/trending/movie/week"
+	case "popular_movie":
+		return "/movie/popular"
+	case "popular_tv":
+		return "/tv/popular"
+	case "top_rated_movie":
+		return "/movie/top_rated"
+	case "upcoming_movie":
+		return "/movie/upcoming"
+	default:
+		return ""
+	}
+}