chore: bump gitlab-ai-provider to 5.3.1 for GPT-5.4 model support

[vglafirov]

Issue for this PR

Closes #18850

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Bumps gitlab-ai-provider from 5.2.2 to 5.3.1. Version 5.3.1 adds three new OpenAI GPT-5.4 proxy models to MODEL_MAPPINGS:

Model ID	Underlying Model
duo-chat-gpt-5-4	gpt-5.4-2026-03-05
duo-chat-gpt-5-4-mini	gpt-5.4-mini
duo-chat-gpt-5-4-nano	gpt-5.4-nano

These models are defined in the ai-gateway models.yml with proxy_provider: openai and were missing from the provider SDK.

This also requires the companion models.dev PR which adds the model definitions to the gitlab provider and fixes the npm field from the stale scoped @gitlab/gitlab-ai-provider (v4.1.0) to the current gitlab-ai-provider — without that fix, opencode's getSDK falls through the bundled provider check and dynamically installs the old package.

How did you verify your code works?

• Ran bun typecheck — passes
• Ran opencode with OPENCODE_MODELS_PATH pointing to a regenerated models.json containing the new gitlab models and confirmed the GPT-5.4 models load and work without the Unknown model ID error

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found.

The searches returned PR #18849 (the current PR) and two historical PRs from 2024 related to initial GPT-5.4 support (#16503, #16233), but these are unrelated dependency bump PRs, not duplicates of the current bump to version 5.3.1.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍