feat: add OrcaRouter third-party format

[sailt-k]

Summary

Adds OrcaRouter (https://www.orcarouter.ai), an OpenAI-compatible LLM gateway, as a named
third-party format — same pattern as lm-studio/arli. Selecting the "OrcaRouter" format
defaults to the OrcaRouter API endpoint, so users only need to provide their API key.

Changes

• common/adapters.ts: register orcarouter in THIRDPARTY_FORMATS, THIRDPARTY_HANDLERS (→ openai), and FORMAT_LABEL.
• srv/adapter/openai.ts: treat orcarouter as a chat format (chat/completions).
• common/requests/util.ts: default the base URL to https://api.orcarouter.ai/v1 for the orcarouter format (overridable with a custom URL).
• web/pages/Settings/Provider/index.tsx: add "OrcaRouter" to the format dropdown.

Verification

Tested live against OrcaRouter's API (e.g. anthropic/claude-opus-4.8): chat completions
succeed with the handler's payload.

I'm an engineer on the OrcaRouter team.

[continuumai-user2]

hi, is it possible for workflow review and approval?

[sceuick]

Hi there,
I'll add this in the next deployment via the KNOWN_PROVIDERS instead. The adapters are largely replaced by providers.