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>

types/types.go

@@ -131,6 +131,22 @@ type CreateTokenResponse struct {
 	ExpiresAt int64  `json:"expires_at"`
 }
 
+// Resource Metadata Management API structures (Issue #12)
+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"`
+}
+
+type UpdateResourceMetadataRequest struct {
+	OwnerUUID   *string `json:"owner_uuid,omitempty"`
+	GroupUUID   *string `json:"group_uuid,omitempty"`
+	Permissions *int    `json:"permissions,omitempty"`
+}
+
 // Cluster and member management types
 type Member struct {
 	ID              string `json:"id"`