Add pull_image + list_registries; remove Gruppe 5 (no Volume API)

- pull_image: SYNO.Docker.Image/pull with repository+tag split via
  rpartition; polls image list every 3 s until image appears, 120 s timeout
- list_registries: SYNO.Docker.Registry/get; shows name, URL, active marker
- Gruppe 5 (Volumes) removed from roadmap — SYNO.Docker.Volume does not exist
- CLAUDE.md: tool count 17 → 19, Volumes section removed
- 28 tests all passing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/mcp_synology_container/server.py

@@ -31,6 +31,7 @@ def create_server(config: AppConfig, client: DsmClient) -> FastMCP:
     from mcp_synology_container.modules.images import register_images
     from mcp_synology_container.modules.networks import register_networks
     from mcp_synology_container.modules.projects import register_projects
+    from mcp_synology_container.modules.registries import register_registries
     from mcp_synology_container.modules.system import register_system
 
     register_projects(mcp, config, client)
@@ -39,6 +40,7 @@ def create_server(config: AppConfig, client: DsmClient) -> FastMCP:
     register_images(mcp, config, client)
     register_system(mcp, config, client)
     register_networks(mcp, config, client)
+    register_registries(mcp, config, client)
 
     logger.info("MCP server configured with all tool modules")
     return mcp