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/dto/billing.dto.ts

@@ -144,6 +144,12 @@ export class CalculateCostDto {
   @IsBoolean()
   enableElasticsearch?: boolean;
 
+  @ApiPropertyOptional({ type: OptionalServiceResourcesDto, description: 'Per-database CPU/RAM/storage limits' })
+  @IsOptional()
+  @ValidateNested()
+  @Type(() => OptionalServiceResourcesDto)
+  databaseResources?: OptionalServiceResourcesDto;
+
   @ApiPropertyOptional({ type: OptionalServiceResourcesDto })
   @IsOptional()
   @ValidateNested()
@@ -213,6 +219,12 @@ export class UpgradeResourcesDto {
   @IsString()
   appStorageSize?: string;
 
+  @ApiPropertyOptional({ type: OptionalServiceResourcesDto, description: 'Database resource limits' })
+  @IsOptional()
+  @ValidateNested()
+  @Type(() => OptionalServiceResourcesDto)
+  databaseResources?: OptionalServiceResourcesDto;
+
   @ApiPropertyOptional({ type: OptionalServiceResourcesDto, description: 'Managed Redis resource limits' })
   @IsOptional()
   @ValidateNested()