feat(chat): enhance search functionality and message highlighting

- Added search match navigation to allow users to cycle through search results in chat sessions.
- Implemented highlighting of search terms in chat messages for better visibility.
- Updated sidebar to display match counts for sessions based on search results.
- Enhanced session search logic in the database to include match counts for improved user experience.
- Refactored chat message component to support dynamic highlighting of search terms.

hooks/use-chat-storage.ts

@@ -10,6 +10,7 @@ export interface SessionSummary {
   updated_at: string;
   preview: string;
   platform: string;
+  match_count?: number;
 }
 
 const TITLE_MODEL = "qwen2.5:0.5b";