fix(gitlab): publish duo-chat-haiku-5-5 in v1 api - #11474

Publishes GitLab Duo's Claude Haiku 5.5 (duo-chat-haiku-5-5) in the v1 API.

The file was marked v2_only = true because no opencode release mapped the model yet. opencode (both v1 and dev) loads its catalog from v1 api.json, so the model doesn't appear in the picker. gitlab-ai-provider has mapped it since 6.22.0. opencode is moving to 6.23.0 in anomalyco/opencode#58998 (v1) and anomalyco/opencode#58999 (dev).

• Removes v2_only = true and updates the header comment. No other fields change.
• After this, every GitLab model is in v1. duo-chat-haiku-5-5 is published with 1,000,000 context, 128,000 output and reasoning (adaptive toggle, low to max effort), as already defined.
• bun validate passes.

Merge order: please merge only after #58998 and #58999 are in released opencode builds. On releases pinned to gitlab-ai-provider 6.19.0 the model would show in the picker but fail with Unknown model ID.

Source (ai-assist models.yml):

- name: "Claude Haiku 5.5"
  gitlab_identifier: "claude_haiku_5_5"
  max_context_tokens: 1_000_000
  proxy_provider: anthropic
  params:
    model: "claude-haiku-5-5"
    max_tokens: 128_000