v0.4.0

Open Responses Spec Compatibility

This release adds full Open Responses spec support, completing all 3 phases of #60.

Added

• Metadata preservation for lossless A→IR→A round-trip across all 4 providers (#60, PR #119)
• Open Responses spec extensions (PR #120):
  • "open_responses" provider alias (same converter as openai_responses)
  • allowed_tools request field passthrough
  • Reasoning content field preservation (distinct from summary)
  • Slug-prefixed extension items opaque round-trip (e.g. openai:web_search_call)
  • OpenResponses-Version header forwarding in gateway

Fixed

• Open Responses compliance tests: 6/6 passing (streaming + non-streaming schema validation)
• Anthropic: preserve stop_sequence, container, citations
• OpenAI Chat: preserve annotations, refusal
• Google GenAI: preserve promptTokensDetails

Full Changelog: v0.3.1...v0.4.0