feat(deploy): configurable CPU/RAM/disk for app databases

Let users size the database workload from the deploy wizard the same way
Redis/RabbitMQ are configured: a resource card (CPU request/limit, memory
request/limit, storage) on the Resources step, stored in
optionalServiceResources.database.

- entity/DTO: add `database` to optionalServiceResources
- k8s: resolveDatabaseResources() applies user-selected resources on both
  the Helm and K8s-API deploy paths (was hardcoded 100m/256Mi→500m/512Mi)
- billing: bill database CPU/RAM as a separate line on top of the app's
  resources; merge it through the upgrade path too
- wizard: db resource card on the Resources step, disk moved into the card,
  cost preview + review summary include the database resources

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/applications/entities/application.entity.ts

@@ -82,9 +82,16 @@ export class Application {
   @Column({ type: 'jsonb', nullable: true })
   logPaths: string[]; // Custom log paths to collect (e.g., ['/app/logs/*.log'])
 
-  /** User-selected CPU/RAM/storage per optional service (redis, rabbitmq). */
+  /** User-selected CPU/RAM/storage per optional service (database, redis, rabbitmq). */
   @Column({ type: 'jsonb', nullable: true })
   optionalServiceResources?: {
+    database?: {
+      cpuRequest?: string;
+      cpuLimit: string;
+      memoryRequest?: string;
+      memoryLimit: string;
+      storageGi: number;
+    };
     redis?: {
       cpuRequest?: string;
       cpuLimit: string;