feat(015): SQL query interface for agents + split read/write pools
Split Connection Pools:
- writeDB: MaxOpenConns=1, serializes all writes (no SQLITE_BUSY)
- readDB: MaxOpenConns=8, query_only=ON, for all SELECTs
- QueryDB() helper returns read pool when available
SQL Query Interface:
- New 'query' action via execute MCP tool
- Read-only enforcement (PRAGMA query_only=ON + SQL validation)
- Curated views: my_messages, my_channels, channel_messages
- Per-agent access control via CTE injection
- Auto LIMIT 100, 5s timeout, SELECT-only validation
- Blocks: INSERT, UPDATE, DELETE, DROP, PRAGMA, etc.
- 12 new tests (access control, validation, limits, CTEs)
Migration 016: agent query views (v_agent_messages, etc.)
Action registry: 30 actions (was 29, added 'query')
All 29 test packages pass.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
