[FEATURE]: Bump gitlab-ai-provider to 6.19.0 (adds Claude Sonnet 5.5 and GPT-6.1 Sol) #53343

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Describe the enhancement you want to request

Bump the pinned gitlab-ai-provider dependency from 6.18.0 to 6.19.0 (latest on npm):

• dev: packages/core and packages/opencode
• v2: packages/core

6.19.0 adds model mappings for two models the GitLab AI Gateway now serves:

• duo-chat-sonnet-5-5 → Claude Sonnet 5.5 (claude-sonnet-5-5), plus duo-workflow-sonnet-5-5 for Agent Platform
• duo-chat-gpt-6-1-sol → GPT-6.1 Sol (gpt-6.1-sol, Responses API)

The models.dev entries for both already landed in anomalyco/models.dev#8475, so they show up in the GitLab model picker today, but selecting them fails with Unknown model ID ... Model must be registered in MODEL_MAPPINGS until opencode ships the new provider.

There are no API changes. It's a dependency bump plus bun.lock.