Test: verify database schema creation and earnings CRUD

[GeiserX]

Context

CashPilot uses SQLite for earnings storage and configuration. The database module should be tested to prevent regressions.

Task

1. Write tests using an in-memory SQLite database
2. Verify schema creation succeeds (tables: earnings, health_events, nodes, etc.)
3. Test earnings insert and query (insert a row, query it back)
4. Test config CRUD operations

Reference

• app/database.py — database module