chore: update gitlab-ai-provider to 3.1.1 and remove unused parameter

[vglafirov]

What does this PR do?

This PR fixes the issue when Gitlab provider falls back to the default model. Models mapping logic moved to gitlab-ai-provider package. OpenCode doesn't provide anthropicModel parameter to agenticChat functioin anymore.

Related issue: https://github.com/anomalyco/opencode/issues/8367

How did you verify your code works?

Tested locally.

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