Add build infrastructure and QUICKSTART guide

- Build script (scripts/build.mjs) using esbuild with iterative stub creation
- Stubs for Bun compile-time intrinsics (feature(), MACRO, bun:bundle)
- Stub modules for feature-gated internal code paths
- QUICKSTART.md with 3 build options (pre-built, esbuild, Bun)
- tsconfig.json, package.json for build tooling

Build reaches ~95% — 108 remaining feature-gated modules need Bun runtime
for full dead code elimination. See QUICKSTART.md for details.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tsconfig.json

@@ -0,0 +1,36 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true,
+    "strict": false,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "jsx": "react-jsx",
+    "outDir": "dist",
+    "rootDir": "src",
+    "baseUrl": ".",
+    "paths": {
+      "bun:bundle": ["stubs/bun-bundle.ts"],
+      "src/*": ["src/*"]
+    },
+    "types": ["node"],
+    "lib": ["ES2022", "DOM"],
+    "allowImportingTsExtensions": false,
+    "noEmit": false
+  },
+  "include": [
+    "src/**/*",
+    "stubs/**/*"
+  ],
+  "exclude": [
+    "node_modules",
+    "dist"
+  ]
+}