fix: correct state destructuring and document headless mode

- Fix extractCodeFromInput destructuring: returns { code, state } not
  { code, extractedState }, so state validation was being bypassed
- Add --no-browser hint to CLI banner for discoverability
- Document --no-browser mode in README.md and CLAUDE.md
- Add test:oauth script to package.json
- Add OAuth test to run-all.cjs test suite

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -26,7 +26,8 @@
     "test:interleaved": "node tests/test-interleaved-thinking.cjs",
     "test:images": "node tests/test-images.cjs",
     "test:caching": "node tests/test-caching-streaming.cjs",
-    "test:crossmodel": "node tests/test-cross-model-thinking.cjs"
+    "test:crossmodel": "node tests/test-cross-model-thinking.cjs",
+    "test:oauth": "node tests/test-oauth-no-browser.cjs"
   },
   "keywords": [
     "claude",