feat(aggregator): add post title support to Kagi News aggregator

- CovesClient.create_post() accepts optional title parameter
- Kagi aggregator now passes story titles to posts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[e-mail]>

aggregators/kagi-news/src/coves_client.py

···
         community_handle: str,
         content: str,
         facets: List[Dict],
+        title: Optional[str] = None,
         embed: Optional[Dict] = None
     ) -> str:
         """
···
             community_handle: Community handle (e.g., "world-news.coves.social")
             content: Post content (rich text)
             facets: Rich text facets (formatting, links)
+            title: Optional post title
             embed: Optional external embed
 
         Returns:
···
                 "content": content,
                 "facets": facets
             }
+
+            # Add title if provided
+            if title:
+                post_data["title"] = title
 
             # Add embed if provided
             if embed:

aggregators/kagi-news/src/main.py

···
                 try:
                     post_uri = self.coves_client.create_post(
                         community_handle=feed_config.community_handle,
+                        title=story.title,
                         content=rich_text["content"],
                         facets=rich_text["facets"],
                         embed=embed