[Feat] Add custom request fields for OpenAI-compatible providers

[zoomote]

​Created by Roomote. Follow up by mentioning @roomote, in the web UI, or in Discord.

What changed

OpenAI-compatible provider profiles now include a localized Extra Body JSON editor for provider-specific request fields. Zoo Code validates the JSON, rejects runtime-managed and prototype-sensitive keys, persists it only for OpenAI-compatible profiles, and merges safe fields into streaming, non-streaming, O-family, and single-completion requests.

The settings control uses VS Code-themed components, accessible validation feedback, translations for every supported locale, and unclipped full-height visual baselines for dark, light, high-contrast, and high-contrast-light themes. The visual tests apply each theme after the shared gallery mount so every baseline exercises its intended VS Code theme.

The changed-code mutation runner now discovers related tests through each package's Vitest binary, and focused assertions cover the Extra Body copy, placeholder, ARIA relationships, reserved-key formatting, and non-OpenAI bypass required by the current mutation gate on main.

Why this change was made

Providers such as Sail Research require request-body metadata to select features such as the balanced completion window. Custom headers cannot express those fields, so users previously needed a proxy. This closes #1104.

Impact

Users can configure provider-specific fields such as { "metadata": { "completion_window": "balanced" } } directly in an OpenAI-compatible profile without allowing custom JSON to override Zoo Code's model, messages, tools, streaming, reasoning, temperature, or token limits.

Related PRs

• Zoo-Code-Docs guide: [Docs] Explain OpenAI-compatible custom request fields Zoo-Code-Docs#46

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[github-actions]

Review process

This PR was opened by an automated account. A human maintainer must verify the change intent, provenance, and validation before merging.

1. Required CI checks pass.
2. The workflow starts CodeRabbit automatically.
3. For eligible human-authored PRs, CodeRabbit reviews and approves the latest commit.
4. A human maintainer reviews and approves after CodeRabbit.

Current step: Ready for human maintainer review and approval.

[zoomote]

Rebased onto current main and pushed 6b437a1. Fixed the gallery theme-order regression, refreshed all five authoritative OpenAI-compatible baselines, repaired package-local mutation-test discovery from the newly merged gate, and strengthened focused tests until changed-code mutation testing had no surviving or uncovered mutants. All current CI checks pass, including webview/extension-host visuals, all four theme fixtures, mutation testing, Ubuntu, Windows, E2E, compile, translations, CodeQL, and Codecov. The PR is mergeable and now awaits human maintainer review/approval. Delegated browser proof was not used because it exceeded the shared proof deadline.