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.

types/types.go

@@ -131,6 +131,23 @@ type CreateTokenResponse struct {
 	ExpiresAt int64  `json:"expires_at"`
 }
 
+// Resource Metadata Management API structures
+type UpdateResourceMetadataRequest struct {
+	OwnerUUID   string `json:"owner_uuid,omitempty"`
+	GroupUUID   string `json:"group_uuid,omitempty"`
+	Permissions int    `json:"permissions,omitempty"`
+	TTL         string `json:"ttl,omitempty"`
+}
+
+type GetResourceMetadataResponse struct {
+	OwnerUUID   string `json:"owner_uuid"`
+	GroupUUID   string `json:"group_uuid"`
+	Permissions int    `json:"permissions"`
+	TTL         string `json:"ttl"`
+	CreatedAt   int64  `json:"created_at"`
+	UpdatedAt   int64  `json:"updated_at"`
+}
+
 // Cluster and member management types
 type Member struct {
 	ID              string `json:"id"`
@@ -277,4 +294,4 @@ type Config struct {
 	// Anonymous access control (Issue #5)
 	AllowAnonymousRead     bool `yaml:"allow_anonymous_read"`     // Allow unauthenticated read access to KV endpoints
 	AllowAnonymousWrite    bool `yaml:"allow_anonymous_write"`    // Allow unauthenticated write access to KV endpoints
-}
+}