fix: prune RPM metadata when a local file is evicted

Evicting or deleting a local RPM removed the local_files row but left its
rpm_metadata behind, so generated repodata kept listing a package that no
longer exists. Deletes now run a provider cleanup hook symmetric to the
existing upload hook.

- add PostDeleteHook and MetadataDeleter provider interfaces, plus a
  DeleteRPMMetadata DB method
- implement AfterDelete in the RPM provider to drop the metadata row
- route both local delete paths (evictLocal and the files handler) through
  a shared deleteLocalFile helper that removes the file then runs the hook
- cover the cleanup with a dockerised test

internal/provider/provider.go

@@ -53,10 +53,20 @@ type PostUploadHook interface {
 	AfterUpload(ctx context.Context, repoName, storagePath, contentHash string, blobs BlobReader, db MetadataStore)
 }
 
+// PostDeleteHook lets a provider clean up derived state (e.g. RPM metadata that
+// feeds generated repodata) after a local file is removed.
+type PostDeleteHook interface {
+	AfterDelete(ctx context.Context, repoName, storagePath string, db MetadataDeleter) error
+}
+
 type MetadataStore interface {
 	InsertRPMMetadata(ctx context.Context, meta *RPMMetadata) error
 }
 
+type MetadataDeleter interface {
+	DeleteRPMMetadata(ctx context.Context, repoName, filePath string) error
+}
+
 type RPMMetadataReader interface {
 	ListRPMMetadataEntries(ctx context.Context, repoName string) ([]RPMMetadata, error)
 }