Initial scaffold: Beat Pocket MV3 extension

- manifest.json with MV3 config, host permissions for beat-battle.net
- content/detector.ts: route + overlay observer, emits bbp:phase events
- content/layout.ts: defensive mobile-first layout reflow
- content/chat-drawer.ts: bottom-sheet drawer, dispatches synthetic events
  through site's own React-managed textarea + button (preserves auth,
  rate-limit, mute, profanity guards)
- content/util/selectors.ts: text- and role-based fallback chain
- content/util/ws-proxy.ts: lightweight WebSocket instrumentation, no
  payload capture
- content/inject.css: mobile overrides using site's existing --bb-* vars
- background.js: MV3 service worker stub
- package.json + tsconfig.json + esbuild.config.mjs: build pipeline
- icons/: 16/32/48/128 placeholder PNGs (chili-red disc)
- docs/PLAN.md: full V1 architecture, risks, scope
- README.md: scope, dev workflow (load unpacked), tech

esbuild.config.mjs

@@ -0,0 +1,29 @@
+// esbuild config — bundles TS entry to a single content script
+import * as esbuild from 'esbuild';
+import { existsSync, mkdirSync } from 'node:fs';
+
+const isWatch = process.argv.includes('--watch');
+const outdir = 'dist/content';
+
+if (!existsSync(outdir)) mkdirSync(outdir, { recursive: true });
+
+const ctx = await esbuild.context({
+  entryPoints: ['extension/content/index.ts'],
+  bundle: true,
+  format: 'iife',
+  target: 'chrome109',
+  outfile: `${outdir}/index.js`,
+  sourcemap: 'linked',
+  logLevel: 'info',
+  banner: { js: '/* Beat Pocket content script */' },
+});
+
+if (isWatch) {
+  await ctx.watch();
+  console.log('esbuild watching…');
+} else {
+  const r = await ctx.rebuild();
+  await ctx.dispose();
+  if (r.errors.length) process.exit(1);
+  console.log('build complete');
+}