Add API endpoints for resource metadata management (ownership & permissions)

New types: UpdateResourceMetadataRequest and GetResourceMetadataResponse in types.go
    AuthService methods: StoreResourceMetadata and GetResourceMetadata in auth/auth.go
    Handlers: getResourceMetadataHandler and updateResourceMetadataHandler in server/handlers.go
    Routes: /kv/{path}/metadata (GET for read, PUT for update) with auth middleware in server/routes.go

Enables fine-grained control over KV path ownership, group assignments, and POSIX-inspired permissions.

auth/auth.go

@@ -227,4 +227,44 @@ func (s *AuthService) HasUsers() (bool, error) {
 	})
 	
 	return hasUsers, err
-}
+}
+
+// StoreResourceMetadata stores or updates resource metadata in BadgerDB
+func (s *AuthService) StoreResourceMetadata(path string, metadata *types.ResourceMetadata) error {
+	now := time.Now().Unix()
+	if metadata.CreatedAt == 0 {
+		metadata.CreatedAt = now
+	}
+	metadata.UpdatedAt = now
+
+	metadataData, err := json.Marshal(metadata)
+	if err != nil {
+		return err
+	}
+
+	return s.db.Update(func(txn *badger.Txn) error {
+		return txn.Set([]byte(ResourceMetadataKey(path)), metadataData)
+	})
+}
+
+// GetResourceMetadata retrieves resource metadata from BadgerDB
+func (s *AuthService) GetResourceMetadata(path string) (*types.ResourceMetadata, error) {
+	var metadata types.ResourceMetadata
+	
+	err := s.db.View(func(txn *badger.Txn) error {
+		item, err := txn.Get([]byte(ResourceMetadataKey(path)))
+		if err != nil {
+			return err
+		}
+
+		return item.Value(func(val []byte) error {
+			return json.Unmarshal(val, &metadata)
+		})
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return &metadata, nil
+}