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.json

@@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "lib": ["ES2022"],
+    "types": ["node"],
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+    "noImplicitOverride": true,
+    "exactOptionalPropertyTypes": false,
+    "declaration": true,
+    "sourceMap": true,
+    "outDir": "dist",
+    "rootDir": ".",
+    "skipLibCheck": true,
+    "isolatedModules": true,
+    "verbatimModuleSyntax": true
+  },
+  "include": ["src", "test", "bench"]
+}