src/lib: 라이브러리 진입점 + 1.0.0 호환 shim

normalizeToNFC/normalizeToNFD — v1 require('@pieroot/nfd2nfc') 호환 유지.
신규 API: normalizeEntry, scan, shouldNormalize + 타입 export.
tsconfig.lib.json: declaration: true, out/lib/에 .d.ts 생성.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tsconfig.lib.json

@@ -0,0 +1,14 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "module": "CommonJS",
+    "moduleResolution": "node",
+    "outDir": "out/lib",
+    "rootDir": "src",
+    "declaration": true,
+    "declarationMap": true,
+    "types": ["node"]
+  },
+  "include": ["src/lib/**/*", "src/core/**/*"],
+  "exclude": ["node_modules", "out", "dist", "src/core/__tests__"]
+}