feat(text): support Responses API

[XXPermanentXX]

Summary

• add explicit --api <chat|responses> routing to bl text chat, keeping Chat Completions as the default
• map text chat requests and responses to the OpenAI-compatible Responses API
• support Responses built-in tool definitions such as {"type":"web_search"}
• handle Responses streaming terminal events so failed, incomplete, or disconnected streams exit non-zero
• regenerate the Bailian CLI command references

Why

Token Plan Harness models expose built-in tools through the Responses API. The CLI previously only called Chat Completions, so those tools could not be triggered from bl text chat.

Routing remains explicit: there is no automatic protocol fallback or model switching.

Validation

• vp check: 0 errors; 5 warnings already present on the clean origin/main baseline
• Responses unit tests: 7 passed
• text-chat.e2e.test.ts: 7 passed
• full vp test run --reporter=dot: 883 passed, 62 skipped, 22 failed
  • failures are in unrelated live/environment tests: unavailable models, HTTP 401/404 endpoints, and Command Pack timeouts
  • no text chat test failed