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>

stubs/bun-bundle.ts

@@ -0,0 +1,4 @@
+// Stub for bun:bundle — feature() is compile-time in Bun; replaced by build script
+export function feature(_flag: string): boolean {
+  return false
+}

stubs/global.d.ts

@@ -0,0 +1,11 @@
+// Global type for MACRO compile-time constants
+// These are normally injected by Bun's bundler via --define at compile time
+declare const MACRO: {
+  VERSION: string
+  BUILD_TIME: string
+  FEEDBACK_CHANNEL: string
+  ISSUES_EXPLAINER: string
+  NATIVE_PACKAGE_URL: string
+  PACKAGE_URL: string
+  VERSION_CHANGELOG: string
+}

stubs/macros.d.ts

@@ -0,0 +1,15 @@
+/**
+ * Compile-time macros injected by Bun's bundler.
+ * These are replaced with string literals during bundling.
+ * For our source build, we provide runtime values.
+ */
+
+declare const MACRO: {
+  VERSION: string
+  BUILD_TIME: string
+  FEEDBACK_CHANNEL: string
+  ISSUES_EXPLAINER: string
+  NATIVE_PACKAGE_URL: string
+  PACKAGE_URL: string
+  VERSION_CHANGELOG: string
+}

stubs/macros.ts

@@ -0,0 +1,20 @@
+// Global compile-time MACRO constants
+// In the real Bun build, these are injected via --define at compile time.
+// Here we provide runtime values matching the published v2.1.88.
+declare global {
+  const MACRO: {
+    VERSION: string
+    BUILD_TIME: string
+    FEEDBACK_CHANNEL: string
+    ISSUES_EXPLAINER: string
+    ISSUES_EXPLAINER_URL: string
+    FEEDBACK_CHANNEL_URL: string
+    NATIVE_PACKAGE_URL: string | null
+    PACKAGE_URL: string
+    VERSION_CHANGELOG: string
+  }
+}
+
+// This is never actually executed — the global is set in the entrypoint wrapper.
+// But we need it so TypeScript doesn't complain about `MACRO` being undeclared.
+export {}