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/deployment.yaml

@@ -28,6 +28,11 @@ spec:
               value: /secrets/claude
             - name: OPENCODE_CONFIG_DIR
               value: /secrets/opencode
+            - name: DATABASE_URL
+              valueFrom:
+                secretKeyRef:
+                  name: harness-db-credentials
+                  key: database-url
           volumeMounts:
             - name: workspace
               mountPath: /data/harness