fix(channel): harden About-enrich edge cases from review

- apply_channel_details: (branding.get("channel") or {}) so a "channel": null
  in brandingSettings can't AttributeError-abort the enrich batch.
- topicLabels: drop empty labels so a malformed topic URL can't render a blank chip.

backend/app/sync/subscriptions.py

@@ -69,7 +69,7 @@ def apply_channel_details(db: Session, items: list[dict]) -> None:
         channel.banner_url = branding.get("image", {}).get("bannerExternalUrl")
         channel.external_links = _external_links(branding)
         channel.topic_categories = topics.get("topicCategories")
-        channel.keywords = branding.get("channel", {}).get("keywords")
+        channel.keywords = (branding.get("channel") or {}).get("keywords")
         channel.details_synced_at = now
 
 

frontend/src/components/ChannelPage.tsx

@@ -38,7 +38,8 @@ function topicLabels(urls: string[]): string[] {
     } catch {
       /* keep raw */
     }
-    seen.add(label.replace(/_/g, " "));
+    label = label.replace(/_/g, " ").trim();
+    if (label) seen.add(label);
   }
   return [...seen];
 }