[FEATURE]: Add reasoning variants for GitLab Duo models #47304

Feature hasn't been suggested before.

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Describe the enhancement you want to request

gitlab-ai-provider 6.14.0 supports reasoning effort controls for GitLab-hosted GPT and Claude models, but OpenCode does not currently generate provider options for that package.

OpenCode should expose the efforts declared by models.dev, map GPT efforts to reasoningEffort, and map Claude efforts to adaptive thinking. This would make the variants available without requiring users to duplicate them in opencode.jsonc.

Related metadata: anomalyco/models.dev#6276
Provider support: https://gitlab.com/vglafirov/gitlab-ai-provider/-/merge_requests/36