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

server/providers/registry.mjs

@@ -15,7 +15,17 @@
 
 /** @typedef {'yt'|'dm'|'tw'|'pt'|'od'|'ru'} ProviderId */
 
-/** @type {Record<ProviderId, { id: ProviderId, label: string, search: (q: string, opts: { limit: number, page?: number }) => Promise<Suggestion[]> }>} */
+import channelRegistry from './channel-registry.mjs';
+
+/**
+ * @typedef {Object} ProviderAdapter
+ * @property {ProviderId} id
+ * @property {string} label
+ * @property {(q: string, opts: { limit: number, page?: number, sort?: string }) => Promise<Suggestion[]>} search
+ * @property {(externalId: string, ctx?: any) => Promise<any=} } [fetchChannelById]
+ */
+
+/** @type {Record<ProviderId, ProviderAdapter>} */
 export const providerRegistry = {
   /** @type {any} */ yt: (await import('./youtube.mjs')).default,
   /** @type {any} */ dm: (await import('./dailymotion.mjs')).default,
@@ -25,6 +35,13 @@ export const providerRegistry = {
   /** @type {any} */ ru: (await import('./rumble.mjs')).default,
 };
 
+for (const [pid, adapter] of Object.entries(providerRegistry)) {
+  const channelAdapter = channelRegistry[/** @type {ProviderId} */(pid)];
+  if (channelAdapter && typeof channelAdapter.fetchChannelById === 'function' && !adapter.fetchChannelById) {
+    adapter.fetchChannelById = channelAdapter.fetchChannelById;
+  }
+}
+
 /**
  * Validate and normalize a comma separated providers list
  * @param {string} input