[FEATURE]: Add a native V2 replacement for provider model filtering

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement

OpenCode V1 supports per-provider model filtering with whitelist and blacklist:

{
  "provider": {
    "ollama-cloud": {
      "whitelist": ["glm-5.2"]
    }
  }
}

This is useful when a provider exposes a large or changing catalog.

V2 currently drops these fields during V1-to-V2 normalization. The provider remains available, but the model filter is not applied.

Reproduction

Tested with @opencode/cli@2.0.9 using a clean config and:

npx --yes @opencode/cli@2.0.9 \
  api --standalone --print-logs get /api/config

The normalized config contains the provider settings but omits whitelist. The server log reports:

path=$.provider.ollama-cloud.whitelist
kind=unsupported
action="omitted unsupported legacy setting"

Expected behavior

Please either:

1. provide a native V2 equivalent for per-provider model filtering; or
2. document the intentional removal and recommended replacement clearly in the V2 migration guide.

The old provider documentation still documents this feature, which makes migration unclear.

References

• V1 documentation: https://opencode.ai/docs/providers#hiding-models
• V2 provider documentation: https://opencode.ai/v2/docs/providers
• V2 migration guide: https://opencode.ai/v2/docs/migrate-v1#accepted-but-unsupported-fields
• V2 normalizer: https://github.com/anomalyco/opencode/blob/v2.0.9/packages/core/src/config/normalize.ts#L54
• V2 unsupported-field handling: https://github.com/anomalyco/opencode/blob/v2.0.9/packages/core/src/config/normalize.ts#L566-L576
• Original V1 implementation: https://github.com/anomalyco/opencode/blob/c0d9f21c0f921b6baf2e034ed64133af04d5b7fb/packages/opencode/src/provider/provider.ts#L449-L475

Related: #42535 covers wildcard support for the existing V1 filter syntax. This issue concerns the missing V2 migration path.

Start with packages/core/src/config/normalize.ts around the V1-to-V2 provider normalization and unsupported-field handling, then compare the linked V1 provider implementation and V2 provider and migration documentation. Confirm how provider model filtering should work in V2; done means the behavior is supported natively or its removal and replacement are clearly documented, with coverage for the reported normalization case.