fix(ci): re-enable claudebox Kaniko cache after registry cleanup

Registry was full (29.4GB/30GB) causing DIGEST_INVALID on all image pushes.
Cleaned old test project repos, expanded PVC from 30Gi to 80Gi, re-enabled cache.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.woodpecker.yml

@@ -57,7 +57,7 @@ steps:
         - ${CI_COMMIT_SHA:0:8}
       context: .
       dockerfile: Dockerfile
-      cache: false
+      cache: true
       skip_tls_verify: true
     when:
       <<: *when_main