Features:
- LLM tool calling for web search decisions (replaces pattern-based)
- QueryRouter with OpenAI function calling for semantic web search
- Tavily rate limiting with monthly tracking and auto-disable at 95%
- Usage stats display in Settings with progress bar

Fixes:
- Backfill now checks disk when DB is empty for screenshots
- Backfill reprocesses hours marked "success" but missing notes
- Backfill interval reduced to 30 minutes (was 1 hour)
- Fixed internal LLM reasoning leaking into answers
- Fixed citation display in MessageThread

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>