fix: register V2 provider through provider.transform

[algonacci]

Summary

The OpenCode 2.x entrypoint no longer loads on current OpenCode. @opencode/plugin 2.0.4 (2026-09-16) removed ctx.catalog, so setup throws:

failed to load plugin  plugin.id=orvix  cause="TypeError: undefined is not an object (evaluating 'ctx.catalog.transform')"

After that error every orvix/* model reports Model unavailable. The V2 support from #4 targeted 2.0.2, which still had catalog.

This PR makes two changes:

• Register through ctx.provider.transform. If the provider does not exist yet, the plugin calls add({ info, models }). If the user already configured it, the plugin fills in missing provider fields with update and appends its models with models.set. User-configured provider fields and models are still never overwritten. Each model record now carries id (the OpenCode key), modelID (the exact upstream id, so managed orvix/* and BYOK ids still go upstream verbatim), and providerID.
• Put reasoning variants in body. Variants stored reasoning_effort under settings, which configures the provider package and is never sent in the request. Selecting orvix/muse-spark-1.3#high therefore sent no reasoning_effort. Variants now use body.

The test fakes now mirror the provider editor. AGENTS.md and the README no longer mention the catalog API. A patch changeset is included.

Verification

• npm run check: typecheck clean, 58/58 tests pass.
• npm run package: passes.
• End-to-end on OpenCode 2.0.21 (opencode run --standalone, isolated XDG dirs) against a local mock OpenAI-compatible server, with providers.orvix.settings.baseURL pointing at the mock:
  • Before: the plugin fails to load and orvix/glm-5.3-flash is unavailable.
  • After: the plugin loads, and requests reach /v1/chat/completions with model: "orvix/muse-spark-1.3" / "orvix/glm-5.3-flash" and a bearer key. The user's baseURL override is respected.
  • -m orvix/muse-spark-1.3#high now sends reasoning_effort: "high". Models without variants send none.
• Not tested against the live Orvix API.

Checklist

• The change is focused and contains no unrelated churn.
• Tests pass with npm run check.
• Packaging passes with npm run package.
• User-visible changes include a Changeset; otherwise, this is not applicable.
• Relevant documentation is updated; otherwise, this is not applicable.

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