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

src/app/shared/models/video-item.model.ts

@@ -1,3 +1,5 @@
+import type { ChannelMeta } from './channel.model';
+
 export interface VideoItem {
   id: string; // id vidéo canonicalisé
   provider: 'youtube' | 'dailymotion' | 'twitch' | 'peertube' | 'odysee' | 'rumble';
@@ -5,6 +7,9 @@ export interface VideoItem {
   thumbnailUrl: string;
   durationSec?: number;
   channelName?: string;
+  channelExternalId?: string;
+  channelAvatarUrl?: string;
+  channelMeta?: ChannelMeta;
   viewCount?: number;
   publishedAt?: string; // ISO
   // Provider-specific routing hints