feat(sync): sélecteur de chaîne YouTube (multi-chaînes/marque) via PageId

server/db.mjs

@@ -1397,6 +1397,12 @@ function ensureOAuthTables() {
       PRIMARY KEY (user_id, provider)
     );`);
     db.exec(`CREATE INDEX IF NOT EXISTS idx_oauth_connections_user ON oauth_connections(user_id);`);
+    // Chaîne YouTube sélectionnée (multi-chaînes / marque) : ajout idempotent.
+    try {
+      const cols = db.prepare(`PRAGMA table_info(oauth_connections)`).all().map((c) => c.name);
+      if (!cols.includes('yt_channel_id')) db.exec(`ALTER TABLE oauth_connections ADD COLUMN yt_channel_id TEXT`);
+      if (!cols.includes('yt_page_id')) db.exec(`ALTER TABLE oauth_connections ADD COLUMN yt_page_id TEXT`);
+    } catch {}
   } catch {}
 }
 ensureOAuthTables();
@@ -1417,9 +1423,19 @@ function oauthRowToDto(row, withTokens = false) {
     dto.accessToken = row.access_token || null;
     dto.refreshToken = row.refresh_token || null;
   }
+  dto.ytChannelId = row.yt_channel_id || null;
+  dto.ytPageId = row.yt_page_id || null;
   return dto;
 }
 
+export function setOAuthChannel(userId, provider, { channelId, pageId }) {
+  ensureOAuthTables();
+  db.prepare(`UPDATE oauth_connections SET yt_channel_id = ?, yt_page_id = ?, updated_at = ?
+    WHERE user_id = ? AND provider = ?`)
+    .run(channelId || null, pageId || null, Date.now(), userId, provider);
+  return getOAuthConnection(userId, provider);
+}
+
 export function upsertOAuthConnection({ userId, provider, externalUserId, displayName, avatarUrl, accessToken, refreshToken, expiresAt, scopes }) {
   ensureOAuthTables();
   const now = Date.now();