docs: fix Gemini provider auth docs to match mutually-exclusive behavior (#6341)

# What does this PR do?

Fixes #5970.

The Gemini provider documentation and the `GeminiConfig` class docstring
described `access_token` as being "used instead of api_key" and stated
that
"when both are set, `access_token` takes precedence". This contradicts
the
actual behavior enforced by `GeminiConfig._validate_auth`, which:

- raises a `ValueError` when **both** `api_key` and `access_token` are
set
  (they are **mutually exclusive**), and
- requires `project` to be set whenever `access_token` is used.

This PR updates the `access_token` `Field` description and the
`GeminiConfig`
docstring so they accurately describe the validation behavior, and
regenerates the provider docs via `scripts/provider_codegen.py`.

## Changes

- `src/ogx/providers/remote/inference/gemini/config.py`: correct the
class
  docstring and the `access_token` field description.
- `docs/docs/providers/inference/remote_gemini.mdx`: regenerated to
match.

## Test Plan

- Docs-only / description-only change; no runtime behavior is modified.
- Ran `./scripts/provider_codegen.py` (via the codegen group) and
confirmed
the regenerated `remote_gemini.mdx` matches the updated field
description
  with no other diffs.

Made with [Cursor](https://cursor.com)

Signed-off-by: Aawegg <aawegbhaladhare03@gmail.com>
Co-authored-by: Matthew Farrellee <matt@cs.wisc.edu>

Author: Aawegg

docs/docs/providers/inference/remote_gemini.mdx

@@ -38,7 +38,7 @@ Google Gemini inference provider for accessing Gemini models and Google's AI ser
 | `network.limits.max_connections` | `int \| None` | No | 100 | Maximum number of concurrent connections in the pool. None means no limit. Values must be >= 1 if set. |
 | `network.limits.max_keepalive_connections` | `int \| None` | No | 20 | Maximum number of idle keep-alive connections to retain. None means no limit. Values must be >= 0 if set. |
 | `network.limits.keepalive_expiry` | `float \| None` | No | 5.0 | Time in seconds to keep idle keep-alive connections open before closing them. None means no expiry. Values must be >= 0 if set. |
-| `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,