Replace all in-memory Map-backed stores (credentials, models, agents,
tasks, iterations, usage) with Drizzle ORM queries against the
homelab-pg PostgreSQL cluster. All store functions are now async.
- Add 6 harness_* tables to @homelab/db schema
- Generate and apply initial Drizzle migration
- Add lazy DB connection proxy to avoid build-time errors
- Wire DATABASE_URL from sealed secret into harness deployment
- Update all API routes, orchestrator, executor, and boot to await
async store operations
