fix: add database indexes for performance optimization
Closes #1
Add two indexes to improve query performance:
- idx_status_startedAt: Speeds up feed queries that ORDER BY startedAt DESC
- idx_status_authorDid_startedAt: Speeds up user status queries with WHERE authorDid = ? ORDER BY startedAt DESC
These indexes will significantly improve performance as the status table grows,
especially important now with infinite scrolling on the feed page.