feat(anthropic): translate output_config/output_format to response_format

[idemerge]

Summary

Anthropic's Messages API gained structured outputs in GA on 2025-11-14 via output_config.format, with an earlier beta path using output_format (behind anthropic-beta: structured-outputs-2025-11-13). The AnthropicTransformer previously dropped both fields silently, so any client using structured outputs against an OpenAI-compatible backend (GLM, DeepSeek, Groq, vLLM, etc.) would degrade to free-form text.

This PR translates both shapes into the unified response_format field, matching OpenAI's structured-outputs schema, so existing provider transformers can pass it through unchanged.

Changes

• packages/core/src/transformer/anthropic.transformer.ts — translate request.output_config?.format ?? request.output_format into result.response_format. Supports json_schema, json_object, and text types. strict defaults to true to mirror Anthropic's guarantee semantics; client can opt out with strict: false.
• packages/core/src/types/llm.ts — add optional response_format union to UnifiedChatRequest.

Test plan

• Type-check (tsc --noEmit) introduces zero new errors over master
• pnpm build passes
• Manual smoke test against an OpenAI-compatible backend:

curl -X POST http://localhost:3456/v1/messages   -H 'Content-Type: application/json'   -H 'x-api-key: ...'   -d '{
    "model": "your-model",
    "max_tokens": 1024,
    "messages": [{"role":"user","content":"List 3 EU capitals."}],
    "output_config": {
      "format": {
        "type": "json_schema",
        "schema": {
          "type": "object",
          "additionalProperties": false,
          "required": ["capitals"],
          "properties": {
            "capitals": {
              "type": "array",
              "items": {
                "type": "object",
                "additionalProperties": false,
                "required": ["country","capital"],
                "properties": {
                  "country": {"type":"string"},
                  "capital": {"type":"string"}
                }
              }
            }
          }
        }
      }
    }
  }'

Expected: content[0].text is a JSON string parseable into an object matching the schema.

Refs

• https://platform.claude.com/docs/en/build-with-claude/structured-outputs
• https://platform.openai.com/docs/guides/structured-outputs

[idemerge]

Before this PR is merged, you can use the plugin (https://github.com/idemerge/ccr-plugin-structured-outputs) to resolve this issue.