fix(kiro): preserve Responses item order

[kaitranntt]

Summary

• finalize an open assistant message before a following function call
• keep client-visible Responses output indices contiguous across reasoning, messages, functions, and hidden server tools
• register the Kiro OpenAI Responses translator
• adapt real Kiro SSE frames and non-stream Claude JSON into the shared converter

Closes #134

Shared translator changes are also proposed upstream in router-for-me/CLIProxyAPI#4429.

Validation

• focused translator tests with actual BuildClaude*Event and BuildClaudeResponse shapes
• focused race tests
• go test -count=1 ./...
• go build ./...
• git diff --check
• independent final review: approved

Docs impact

None. This restores the existing Responses API contract without changing setup or public configuration.