M1: core path escaping, order-preserving index value encoding, errors

Scaffold TypeScript/Vitest project, add DESIGN.md (brief) and CLAUDE.md.
Property tests cover escape round-trips, separator-freedom and order preservation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Qxbkp4tA7G5SCWjzWuxmE

.gitignore

@@ -0,0 +1,4 @@
+node_modules
+dist
+coverage
+*.log