docs: fix Gemini provider auth docs to match mutually-exclusive behavior

The Gemini config docs and class docstring stated that access_token is
"used instead of api_key" and that "when both are set, access_token takes
precedence". This contradicts _validate_auth, which raises a ValueError
when both api_key and access_token are set (they are mutually exclusive)
and also requires project when access_token is used.

Update the access_token Field description and the GeminiConfig docstring to
describe the actual validation behavior, and regenerate the provider docs.

Closes #5970

Signed-off-by: Aawegg <aawegbhaladhare03@gmail.com>

Author: Aawegg

docs/docs/providers/inference/remote_gemini.mdx

@@ -34,7 +34,7 @@ Google Gemini inference provider for accessing Gemini models and Google's AI ser
 | `network.timeout.connect` | `float \| None` | No |  | Connection timeout in seconds. |
 | `network.timeout.read` | `float \| None` | No |  | Read timeout in seconds. |
 | `network.headers` | `dict[str, str] \| None` | No |  | Additional HTTP headers to include in all requests. |
-| `access_token` | `SecretStr \| None` | No |  | OAuth2 access token for Gemini. When set, used instead of api_key for Bearer authentication. |
+| `access_token` | `SecretStr \| None` | No |  | OAuth2 access token for Gemini, used for Bearer authentication. Mutually exclusive with api_key—set one or the other, not both. Requires project to be set. |
 | `project` | `str \| None` | No |  | Google Cloud project ID for quota attribution when using OAuth/ADC credentials. |
 
 ## Sample Configuration

src/ogx/providers/remote/inference/gemini/config.py

@@ -28,12 +28,14 @@ class GeminiConfig(RemoteInferenceProviderConfig):
     Supports either a static API key (``api_key`` / ``GEMINI_API_KEY``) or an
     OAuth2 access token (``access_token`` / ``GEMINI_ACCESS_TOKEN``) for
     short-lived credential injection (e.g. ``gcloud auth application-default
-    print-access-token``).  When both are set, ``access_token`` takes precedence.
+    print-access-token``).  ``api_key`` and ``access_token`` are mutually
+    exclusive—set one or the other, not both. When ``access_token`` is used,
+    ``project`` is also required.
     """
 
     access_token: SecretStr | None = Field(
         default=None,
-        description="OAuth2 access token for Gemini. When set, used instead of api_key for Bearer authentication.",
+        description="OAuth2 access token for Gemini, used for Bearer authentication. Mutually exclusive with api_key—set one or the other, not both. Requires project to be set.",
     )
     project: str | None = Field(
         default=None,