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>

utils/attributionHooks.js

@@ -0,0 +1,3 @@
+// Auto-generated stub
+export default function attributionHooks() {}
+export const attributionHooks = () => {}

utils/systemThemeWatcher.js

@@ -0,0 +1,3 @@
+// Auto-generated stub
+export default function systemThemeWatcher() {}
+export const systemThemeWatcher = () => {}

utils/udsClient.js

@@ -0,0 +1,3 @@
+// Auto-generated stub
+export default function udsClient() {}
+export const udsClient = () => {}