Add Grafana dashboard, monitoring docs, and loosen symbolic filter

[atharvas]

Summary

• Grafana dashboard: Pre-configured dashboard with 30+ panels for monitoring pipeline health, synthesis metrics, dataset growth, and browsing data. Connects to Supabase via a read-only grafana_ro Postgres role. Anonymous viewer access (no login needed), safe for public exposure via ngrok.
• Monitoring docs: New docs/guide/monitoring.md with setup instructions, panel descriptions, and architecture overview.
• Makefile targets: Added supabase-up/down/status, grafana-up/down/logs/migrate convenience targets.
• Symbolic filter improvements: Changed message_filter from AND to OR logic (positive keyword OR no negative keyword), added ~30 new positive keywords (memory, reduce, batch, async, gpu, simd, etc.) and 3 new negatives (docstring, autoupdate, pre-commit). Recomputed is_performance_commit_symbolic column preserving all existing true values.
• Dashboard link: Added live dashboard badge to README.

Test plan

• make grafana-migrate && make grafana-up — Grafana starts at http://localhost:3001
• Dashboard loads without login, all panels render
• uv run pytest tests/test_filters.py — all 66 tests pass
• make help — new targets visible