feat(gemini): improve request context for support and compatibility

Include the Hermes client name and version with Gemini inference, model and tier checks, and TTS requests. Add focused coverage for the request headers and keep the Gemini-specific context scoped to Google Gemini endpoints.

hermes_cli/models.py

@@ -3594,6 +3594,8 @@ def probe_api_models(
 
     tried: list[str] = []
     headers: dict[str, str] = {"User-Agent": _HERMES_USER_AGENT}
+    if urllib.parse.urlparse(normalized).hostname == "generativelanguage.googleapis.com":
+        headers["X-Goog-Api-Client"] = f"hermes-agent/{_HERMES_VERSION}"
     if api_key and api_mode == "anthropic_messages":
         headers["x-api-key"] = api_key
         headers["anthropic-version"] = "2023-06-01"