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

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

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

integration_test/basic_data/badger/KEYREGISTRY

@@ -0,0 +1 @@
+L<EFBFBD>a<1C>M<EFBFBD>N<EFBFBD>A<EFBFBD><41><EFBFBD><EFBFBD><EFBFBD>lHello Badger