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

pnpm-lock.yaml

@@ -72,9 +72,18 @@ importers:
 
   apps/harness:
     dependencies:
+      '@homelab/db':
+        specifier: workspace:^
+        version: link:../../packages/db
+      drizzle-orm:
+        specifier: ^0.36.0
+        version: 0.36.4(@opentelemetry/api@1.9.0)(@types/pg@8.15.6)(@types/react@19.2.14)(postgres@3.4.8)(react@19.2.4)
       next:
         specifier: ^15.1.0
         version: 15.5.14(@opentelemetry/api@1.9.0)(react-dom@19.2.4(react@19.2.4))(react@19.2.4)
+      postgres:
+        specifier: ^3.4.0
+        version: 3.4.8
       react:
         specifier: ^19.0.0
         version: 19.2.4