Fix crawled_at type error in get_channel

SQLite returns datetime columns as strings via raw text() queries.
Parse crawled_at safely before comparing against utcnow().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/routers/channels.py

@@ -579,11 +579,17 @@ def get_channel(
         raise HTTPException(status_code=404, detail="Channel not found")
 
     # Re-index in the background if stale (not crawled in the last hour)
-    crawled_at = row.get("crawled_at")
-    stale = (
-        crawled_at is None
-        or (datetime.utcnow() - crawled_at).total_seconds() > 3600
-    )
+    stale = True
+    try:
+        crawled_at_raw = row.get("crawled_at")
+        if crawled_at_raw:
+            crawled_at = (
+                crawled_at_raw if isinstance(crawled_at_raw, datetime)
+                else datetime.fromisoformat(str(crawled_at_raw))
+            )
+            stale = (datetime.utcnow() - crawled_at).total_seconds() > 3600
+    except Exception:
+        pass
     if stale:
         background_tasks.add_task(_index_channel_task, channel_id, current_user.id)