Migrate harness from in-memory stores to CloudNativePG

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

apps/harness/k8s/base/kustomization.yaml

@@ -5,3 +5,4 @@ resources:
   - service.yaml
   - harness-claude-credentials-sealed.yaml
   - harness-opencode-credentials-sealed.yaml
+  - harness-db-credentials-sealed.yaml