Remove obsolete GCP secret access from mobile CI workflow

The mobile app code analysis workflow is still authenticating to Google Cloud and fetching Firebase-related secrets, but the project has migrated to Azure and no longer uses GCP.

Observed failure:
- Workflow: `.github/workflows/dart-code-metrics.yaml`
- Failing step: `Add firebase options files`
- Error: `gcloud.secrets.versions.access ... NOT_FOUND` for `sta-key-mobile-firebase-options-dev`

Requested cleanup:
- Remove or replace GCP auth and `gcloud secrets` usage in the mobile CI workflow.
- Update the workflow to use the current Azure-based setup, or remove the step entirely if it is no longer needed.
- Verify the workflow still supports mobile code analysis without GCP dependencies.

Open .github/workflows/dart-code-metrics.yaml and inspect the authentication and “Add firebase options files” steps, especially the gcloud secrets command. Check whether the workflow has an existing Azure-based setup or whether the Firebase step is still needed, then run the mobile code analysis workflow. Done means the analysis runs without GCP authentication or secret-fetching failures.

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