fix(channel): titre/URL Dailymotion + playlists et pagination YouTube

- channel-registry DM: retire le champ invalide avatar_url (400 sur toute la requete -> titre null), URL officielle /user/<username>
- channel-content YT: ne plus envoyer pageToken=undefined (400 -> playlists vides); cache de pageTokens opaques pour la pagination videos/shorts/live/playlists
- channel-content.service: stoppe l'infinite scroll quand une page n'apporte rien de nouveau

server/providers/channel-registry.mjs

@@ -86,20 +86,23 @@ async function fetchYoutubeChannel(externalId) {
 
 async function fetchDailymotionChannel(externalId) {
   try {
+    // NOTE : `avatar_url` n'est pas un champ valide de l'API user (400 sur
+    // toute la requête) — seuls avatar_720_url / avatar_medium_url le sont.
     const params = new URLSearchParams({
-      fields: 'id,username,screenname,avatar_720_url,avatar_medium_url,avatar_url,url,followers_total,verified',
+      fields: 'id,username,screenname,avatar_720_url,avatar_medium_url,url,followers_total,verified',
     });
     const data = await fetchWithTimeout(`https://api.dailymotion.com/user/${externalId}?${params.toString()}`);
+    const username = data.username || externalId;
     return safeMeta({
       title: data.screenname || data.username,
       handle: data.username ? `@${data.username}` : undefined,
-      avatarUrl: data.avatar_720_url || data.avatar_medium_url || data.avatar_url,
-      url: data.url,
+      avatarUrl: data.avatar_720_url || data.avatar_medium_url,
+      url: `https://www.dailymotion.com/user/${username}`,
       subsCount: typeof data.followers_total === 'number' ? data.followers_total : undefined,
       verified: Boolean(data.verified),
-    }, { provider: 'dm', externalId, url: `https://www.dailymotion.com/${externalId}` });
+    }, { provider: 'dm', externalId, url: `https://www.dailymotion.com/user/${externalId}` });
   } catch {
-    return { provider: 'dm', externalId, url: `https://www.dailymotion.com/${externalId}` };
+    return { provider: 'dm', externalId, url: `https://www.dailymotion.com/user/${externalId}` };
   }
 }