feat(channel): page details chaine multi-providers avec onglets et infinite scroll

- Strategy Pattern front: ChannelProviderInterface + 6 providers (yt/dm/tw/pt/od/ru) + factory (ids longs/courts)
- ChannelContentService: cache par onglet/tri/recherche (TTL 5min), pagination nextPage
- ChannelPage: header (banniere/avatar/subs/description ...plus), tabs dynamiques par capabilities, grilles videos/shorts 9:16/playlists/live, recherche debounced, tri recent/populaire, infinite scroll IntersectionObserver, skeletons/empty/error
- Backend: GET /api/channels/:provider/:id/content (videos/shorts/playlists/live) natif par provider

db/schema.sql

@@ -19,6 +19,7 @@ CREATE TABLE IF NOT EXISTS user_preferences (
   user_id TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
   language TEXT DEFAULT 'en',
   default_provider TEXT,
+  default_providers TEXT,
   theme TEXT DEFAULT 'system',
   video_quality TEXT DEFAULT 'auto',
   region TEXT,
@@ -83,32 +84,30 @@ CREATE TABLE IF NOT EXISTS watch_history (
 CREATE UNIQUE INDEX IF NOT EXISTS uq_watch_history_user_video ON watch_history(user_id, provider, video_id);
 CREATE INDEX IF NOT EXISTS idx_watch_history_user_time ON watch_history(user_id, watched_at DESC);
 
--- Subscriptions & categories -----------------------------------------------
-CREATE TABLE IF NOT EXISTS categories (
-  id TEXT PRIMARY KEY,
-  user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  name TEXT NOT NULL,
-  created_at TEXT NOT NULL,
-  UNIQUE(user_id, name)
+-- Channels cache & subscriptions --------------------------------------------
+CREATE TABLE IF NOT EXISTS channels (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  provider TEXT NOT NULL,
+  external_id TEXT NOT NULL,
+  title TEXT,
+  handle TEXT,
+  avatar_url TEXT,
+  url TEXT,
+  subs_count INTEGER,
+  verified INTEGER DEFAULT 0,
+  last_refreshed_at INTEGER,
+  UNIQUE(provider, external_id)
 );
 
 CREATE TABLE IF NOT EXISTS subscriptions (
-  id TEXT PRIMARY KEY,
-  user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  provider TEXT NOT NULL,
-  channel_id TEXT NOT NULL,
-  channel_name TEXT,
-  notify INTEGER NOT NULL DEFAULT 0,
-  subscribed_at TEXT NOT NULL,
-  UNIQUE(user_id, provider, channel_id)
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  channel_id INTEGER NOT NULL REFERENCES channels(id) ON DELETE CASCADE,
+  created_at INTEGER NOT NULL,
+  UNIQUE(user_id, channel_id)
 );
 
-CREATE TABLE IF NOT EXISTS subscription_categories (
-  subscription_id TEXT NOT NULL REFERENCES subscriptions(id) ON DELETE CASCADE,
-  category_id TEXT NOT NULL REFERENCES categories(id) ON DELETE CASCADE,
-  PRIMARY KEY (subscription_id, category_id)
-);
-CREATE INDEX IF NOT EXISTS idx_subscriptions_user ON subscriptions(user_id);
+CREATE INDEX IF NOT EXISTS idx_subs_user ON subscriptions(user_id);
 
 -- Playlists -----------------------------------------------------------------
 CREATE TABLE IF NOT EXISTS playlists (