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

tsconfig.build.json

@@ -0,0 +1,5 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": { "rootDir": "src", "outDir": "dist" },
+  "include": ["src"]
+}