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/billing/billing.service.ts

@@ -637,6 +637,16 @@ export class BillingService {
       replicas: newResources.replicas ?? base.replicas,
       ...(newResources.dbStorageSize && { dbStorageSize: newResources.dbStorageSize }),
       ...(newResources.appStorageSize && { appStorageSize: newResources.appStorageSize }),
+      ...(newResources.databaseResources && {
+        databaseResources: {
+          ...base.databaseResources,
+          ...newResources.databaseResources,
+          storageGi:
+            newResources.databaseResources.storageGi ??
+            base.databaseResources?.storageGi ??
+            1,
+        },
+      }),
       ...(newResources.redisResources && {
         redisResources: {
           ...base.redisResources,
@@ -734,7 +744,9 @@ export class BillingService {
         ? (app as Application).optionalServiceResources
         : undefined;
     const dtoExtras =
-      'redisResources' in app ? (app as CalculateCostDto) : undefined;
+      'redisResources' in app || 'databaseResources' in app
+        ? (app as CalculateCostDto)
+        : undefined;
     const productType =
       'productType' in app
         ? ((app as Application).productType ?? ProductType.APPLICATION)
@@ -753,6 +765,7 @@ export class BillingService {
       enableRabbitmq: !!app.enableRabbitmq,
       enableElasticsearch: managed ? false : !!app.enableElasticsearch,
       enableCustomDomain: managed ? false : enableCustomDomain,
+      databaseResources: optionalRes?.database ?? dtoExtras?.databaseResources,
       redisResources: optionalRes?.redis ?? dtoExtras?.redisResources,
       rabbitmqResources: optionalRes?.rabbitmq ?? dtoExtras?.rabbitmqResources,
     };
@@ -919,6 +932,7 @@ export class BillingService {
       enableRabbitmq: config.enableRabbitmq,
       enableElasticsearch: config.enableElasticsearch,
       enableCustomDomain: config.enableCustomDomain,
+      databaseResources: config.databaseResources,
       redisResources: config.redisResources,
       rabbitmqResources: config.rabbitmqResources,
     };