Root cause: _on_mcp_server_connected was defined and registered AFTER
mcp_manager.load_all(), so startup connections never registered their
tools into the ToolRegistry.

Fix: explicitly iterate connected clients after build_default_registries()
creates tool_registry, and register their MCP tools before starting the
health-check loop. The callback stays for future reconnects.

Also adds diagnostic warning in build_tool_list when tools are missing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>