fix(openclaw): use proxy API for google models behind cllama

[mostlydev]

Summary

• route google/* models behind cllama through the proxy API surface instead of Google-native OpenClaw API mode
• keep direct non-cllama Google behavior unchanged
• add regression coverage for both cases

Why

When OpenClaw rewrites google/* providers to http://cllama:8080/v1, it must speak the proxy's OpenAI-compatible surface. google-generative-ai causes OpenClaw to hit the wrong path and return 404 page not found.

What changed

• use a dedicated cllamaModelAPIForProvider() helper inside the cllama rewrite branch
• keep Anthropics on anthropic-messages
• map Google and other non-Anthropic providers behind cllama to openai-completions
• add regression tests for:
  • google/* + cllama => openai-completions
  • direct google/* => no cllama provider rewrite, native Google API behavior preserved

Validation

• go test -run 'TestGenerateConfig(CllamaGoogleUsesOpenAICompletions|DirectGoogleKeepsNativeAPI|CllamaRewritesProviderBaseURL|CllamaRewritesAllModelProviders)' -count=1 ./internal/driver/openclaw
• go test -count=1 ./internal/driver/openclaw
• go test -count=1 ./internal/driver/...

Scope note

I audited the other cllama-aware drivers while fixing this. This specific provider-API mismatch is confined to OpenClaw; the others do not compile the same api field in their cllama path.

Closes #127

[mostlydev]

Addressed the two must-fix review points:

• added an explicit anthropic["api"] == "anthropic-messages" assertion in the existing cllama Anthropic test
• removed the tautological direct-Google helper assertion so the test stays purely behavioral

Re-verified with:

• go test -run 'TestGenerateConfig(CllamaGoogleUsesOpenAICompletions|DirectGoogleKeepsNativeAPI|CllamaRewritesProviderBaseURL|CllamaRewritesAllModelProviders)' -count=1 ./internal/driver/openclaw
• go test -count=1 ./internal/driver/openclaw