feat: implement resource metadata management API (issue #12)

Add API endpoints to manage ResourceMetadata (ownership, groups, permissions)
for KV resources. This enables administrators to configure granular access
control for stored data.

Changes:
- Add GetResourceMetadataResponse and UpdateResourceMetadataRequest types
- Add GetResourceMetadata and SetResourceMetadata methods to AuthService
- Add GET /kv/{path}/metadata endpoint (requires admin:users:read)
- Add PUT /kv/{path}/metadata endpoint (requires admin:users:update)
- Both endpoints protected by JWT authentication
- Metadata routes registered before general KV routes to prevent pattern conflicts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

server/handlers.go

@@ -213,6 +213,104 @@ func (s *Server) deleteKVHandler(w http.ResponseWriter, r *http.Request) {
 	s.logger.WithField("path", path).Info("Value deleted")
 }
 
+// getResourceMetadataHandler retrieves metadata for a KV resource
+func (s *Server) getResourceMetadataHandler(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	path := vars["path"]
+
+	// Get metadata from storage
+	metadata, err := s.authService.GetResourceMetadata(path)
+	if err == badger.ErrKeyNotFound {
+		http.Error(w, "Not Found: No metadata exists for this resource", http.StatusNotFound)
+		return
+	}
+	if err != nil {
+		s.logger.WithError(err).WithField("path", path).Error("Failed to get resource metadata")
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return
+	}
+
+	response := types.GetResourceMetadataResponse{
+		OwnerUUID:   metadata.OwnerUUID,
+		GroupUUID:   metadata.GroupUUID,
+		Permissions: metadata.Permissions,
+		TTL:         metadata.TTL,
+		CreatedAt:   metadata.CreatedAt,
+		UpdatedAt:   metadata.UpdatedAt,
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response)
+}
+
+// updateResourceMetadataHandler updates metadata for a KV resource
+func (s *Server) updateResourceMetadataHandler(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	path := vars["path"]
+
+	// Parse request body
+	var req types.UpdateResourceMetadataRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		http.Error(w, "Bad Request: Invalid JSON", http.StatusBadRequest)
+		return
+	}
+
+	// Get existing metadata or create new one
+	metadata, err := s.authService.GetResourceMetadata(path)
+	if err == badger.ErrKeyNotFound {
+		// Create new metadata with defaults
+		metadata = &types.ResourceMetadata{
+			OwnerUUID:   "",
+			GroupUUID:   "",
+			Permissions: types.DefaultPermissions,
+			TTL:         "",
+			CreatedAt:   time.Now().Unix(),
+			UpdatedAt:   time.Now().Unix(),
+		}
+	} else if err != nil {
+		s.logger.WithError(err).WithField("path", path).Error("Failed to get resource metadata")
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return
+	}
+
+	// Update only provided fields
+	if req.OwnerUUID != nil {
+		metadata.OwnerUUID = *req.OwnerUUID
+	}
+	if req.GroupUUID != nil {
+		metadata.GroupUUID = *req.GroupUUID
+	}
+	if req.Permissions != nil {
+		metadata.Permissions = *req.Permissions
+	}
+	metadata.UpdatedAt = time.Now().Unix()
+
+	// Store updated metadata
+	if err := s.authService.SetResourceMetadata(path, metadata); err != nil {
+		s.logger.WithError(err).WithField("path", path).Error("Failed to update resource metadata")
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return
+	}
+
+	response := types.GetResourceMetadataResponse{
+		OwnerUUID:   metadata.OwnerUUID,
+		GroupUUID:   metadata.GroupUUID,
+		Permissions: metadata.Permissions,
+		TTL:         metadata.TTL,
+		CreatedAt:   metadata.CreatedAt,
+		UpdatedAt:   metadata.UpdatedAt,
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response)
+
+	s.logger.WithFields(logrus.Fields{
+		"path":       path,
+		"owner_uuid": metadata.OwnerUUID,
+		"group_uuid": metadata.GroupUUID,
+	}).Info("Resource metadata updated")
+}
+
 // isClusterMember checks if request is from a cluster member
 func (s *Server) isClusterMember(remoteAddr string) bool {
 	host, _, err := net.SplitHostPort(remoteAddr)