feat: add API key bearer token authentication

- ApiKeyVerifier(TokenVerifier) — validates Authorization: Bearer <key>
  against UNRAID_MCP_API_KEY; guards against empty-key bypass
- _build_auth() replaces module-level _build_google_auth() call:
  returns MultiAuth(server=google, verifiers=[api_key]) when both set,
  GoogleProvider alone, ApiKeyVerifier alone, or None
- settings.py: add UNRAID_MCP_API_KEY + is_api_key_auth_configured()
  + api_key_auth_enabled in get_config_summary()
- run_server(): improved auth status logging for all three states
- tests/test_api_key_auth.py: 9 tests covering verifier + _build_auth
- .env.example: add UNRAID_MCP_API_KEY section
- docs/GOOGLE_OAUTH.md: add API Key section
- README.md / CLAUDE.md: rename section, document both auth methods
- Fix pre-existing: test_health.py patched cache_middleware/error_middleware
  now match renamed _cache_middleware/_error_middleware in server.py

tests/schema/test_query_validation.py

@@ -36,7 +36,7 @@ def _all_domain_dicts(unraid_mod: object) -> list[tuple[str, dict[str, str]]]:
     """
     import types
 
-    m = unraid_mod  # type: ignore[assignment]
+    m = unraid_mod
     if not isinstance(m, types.ModuleType):
         import importlib
 
@@ -417,7 +417,6 @@ class TestDockerQueries:
             "details",
             "networks",
             "network_details",
-            "_resolve",
         }
         assert set(QUERIES.keys()) == expected