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/api/v2/objects.go

@@ -75,7 +75,7 @@ func (h *ObjectsHandler) evictLocal(w http.ResponseWriter, r *http.Request) {
 	repoName := chi.URLParam(r, "name")
 	path := chi.URLParam(r, "*")
 
-	if err := h.db.DeleteLocalFile(r.Context(), repoName, path); err != nil {
+	if err := deleteLocalFile(r.Context(), h.db, repoName, path); err != nil {
 		http.Error(w, fmt.Sprintf("evict failed: %v", err), http.StatusInternalServerError)
 		return
 	}