chore: bump gitlab-ai-provider to 6.19.0 - #53345

Issue for this PR

Closes #53343

Type of change

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

What does this PR do?

Bumps the pinned gitlab-ai-provider from 6.18.0 to 6.19.0 in packages/core and packages/opencode. bun.lock changes only in those two pins and the resolved package entry.

6.19.0 adds the duo-chat-sonnet-5-5, duo-workflow-sonnet-5-5 and duo-chat-gpt-6-1-sol mappings. The models.dev entries already landed in anomalyco/models.dev#8475, so these models appear in the picker but fail with Unknown model ID until this bump ships. That release's only source change is in src/model-mappings.ts, and the API we use didn't change, so no opencode source changes were needed.

How did you verify your code works?

• bun install: both workspace packages resolve gitlab-ai-provider 6.19.0 from npm, and the installed dist/ contains the new model ids.
• bun typecheck passes in packages/core and packages/opencode.
• packages/core: bun test gives 1100 pass, 0 fail.
• packages/opencode: bun test test/provider/gitlab-duo.test.ts test/provider/provider.test.ts test/provider/transform.test.ts gives 687 pass, 0 fail.

Screenshots / recordings

Not a UI change.

Checklist

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