fix(gemini): fail fast on missing API key + surface it in hermes dump (#15133)

Two small fixes triggered by a support report where the user saw a
cryptic 'HTTP 400 - Error 400 (Bad Request)!!1' (Google's GFE HTML
error page, not a real API error) on every gemini-2.5-pro request.

The underlying cause was an empty GOOGLE_API_KEY / GEMINI_API_KEY, but
nothing in our output made that diagnosable:

1. hermes_cli/dump.py: the api_keys section enumerated 23 providers but
   omitted Google entirely, so users had no way to verify from 'hermes
   dump' whether the key was set. Added GOOGLE_API_KEY and GEMINI_API_KEY
   rows.

2. agent/gemini_native_adapter.py: GeminiNativeClient.__init__ accepted
   an empty/whitespace api_key and stamped it into the x-goog-api-key
   header, which made Google's frontend return a generic HTML 400 long
   before the request reached the Generative Language backend. Now we
   raise RuntimeError at construction with an actionable message
   pointing at GOOGLE_API_KEY/GEMINI_API_KEY and aistudio.google.com.

Added a regression test that covers '', '   ', and None.

agent/gemini_native_adapter.py

@@ -801,6 +801,13 @@ class GeminiNativeClient:
         http_client: Optional[httpx.Client] = None,
         **_: Any,
     ) -> None:
+        if not (api_key or "").strip():
+            raise RuntimeError(
+                "Gemini native client requires an API key, but none was provided. "
+                "Set GOOGLE_API_KEY or GEMINI_API_KEY in your environment / ~/.hermes/.env "
+                "(get one at https://aistudio.google.com/app/apikey), or run `hermes setup` "
+                "to configure the Google provider."
+            )
         self.api_key = api_key
         normalized_base = (base_url or DEFAULT_GEMINI_BASE_URL).rstrip("/")
         if normalized_base.endswith("/openai"):