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/peertube.mjs

@@ -44,6 +44,7 @@ const handler = {
           url: item.url,
           thumbnail,
           uploaderName: (item.account && (item.account.displayName || item.account.name)) || undefined,
+          channelId: (item.channel && (item.channel.name || item.channel.uuid)) || (item.account && item.account.name) || undefined,
           type: 'video',
           duration: typeof item.duration === 'number' && item.duration > 0 ? Math.round(item.duration) : undefined
         };