revert(build): remove app build pipeline revamp (Nixpacks/MinIO/Trivy/registry GC)

Reverts commits 3eff38f and c379a23 and restores the previous Kaniko-only
build pipeline (runtime detection + per-runtime Dockerfile generation,
disk-based source upload).

Removed: Nixpacks Dockerfile generation, MinIO source storage (common/storage),
Bull build queue + Redis build state (common/redis, deployment.processor),
Trivy image scan (scan.service, deployment.vulnerabilitySummary), and daily
registry garbage collection (registry-gc). Nothing outside the build/deploy
path depended on these. Backend tsc + 105/106 tests green (the pre-existing
helm.service chartPath failure is unrelated); frontend tsc green.

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

backend/src/build/build.module.ts

@@ -1,6 +1,5 @@
 import { Module, forwardRef } from '@nestjs/common';
 import { BuildService } from './build.service';
-import { ScanService } from './scan.service';
 import { KubernetesModule } from '../kubernetes/kubernetes.module';
 import { ClustersModule } from '../clusters/clusters.module';
 
@@ -9,7 +8,7 @@ import { ClustersModule } from '../clusters/clusters.module';
     forwardRef(() => KubernetesModule),
     ClustersModule,
   ],
-  providers: [BuildService, ScanService],
-  exports: [BuildService, ScanService],
+  providers: [BuildService],
+  exports: [BuildService],
 })
 export class BuildModule {}