Support Claude on Google Vertex AI

[germag]

Problem Statement

OCR cannot use Claude over Vertex AI, because the API is a bit different[0].

[0] https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai

Proposed Solution

Add a OCR_USE_ANTHROPIC_VERTEX=true to use the proper API,

or it can be autodetected using something like:

isVertex := strings.Contains(cfg.URL, "aiplatform.googleapis.com")

(not sure about this one)

Alternatives Considered

No response

Affected Area

CLI / Commands, Review Agent / LLM interaction

Additional Context

I can work on it, if this feature is desirable.