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

extension/content/util/ws-proxy.ts

@@ -0,0 +1,55 @@
+/**
+ * WebSocket instrumentation. We wrap WebSocket.prototype.send so we can:
+ *  1. Observe outgoing chat messages (log only, no payload capture for V1)
+ *  2. Optionally resend synthetic chat messages if the React dispatch
+ *     path is broken (fallback for chat-drawer.send).
+ *
+ * Idempotent — safe to call multiple times.
+ */
+
+interface WSInstrumentation {
+  restore: () => void;
+  sentCount: () => number;
+}
+
+const FLAG = '__beatPocketWSInstrumented__';
+
+export function instrumentWS(): WSInstrumentation {
+  const proto = WebSocket.prototype as unknown as Record<string, unknown>;
+  if (proto[FLAG]) {
+    return existingInstrumentation();
+  }
+  const originalSend = proto.send as (data: string | ArrayBufferLike | Blob | ArrayBufferView) => void;
+  let sent = 0;
+
+  proto.send = function patchedSend(data: unknown): void {
+    sent += 1;
+    try {
+      // Lightweight logging only — we never read or store payload contents.
+      // Just observe that WS frames flow so we know auth is alive.
+      if (typeof data === 'string') {
+        window.dispatchEvent(new CustomEvent('bbp:ws-send', { detail: { len: data.length } }));
+      }
+    } catch {
+      /* never throw out of a wrapped primitive */
+    }
+    return originalSend.call(this, data as never);
+  };
+
+  proto[FLAG] = { originalSend, sent: () => sent, restore: () => restore() };
+
+  function restore() {
+    if (proto[FLAG] && (proto[FLAG] as { originalSend?: unknown }).originalSend) {
+      proto.send = (proto[FLAG] as { originalSend: typeof originalSend }).originalSend;
+      delete proto[FLAG];
+    }
+  }
+
+  return { restore, sentCount: () => sent };
+}
+
+function existingInstrumentation(): WSInstrumentation {
+  const proto = WebSocket.prototype as unknown as Record<string, unknown>;
+  const flag = proto[FLAG] as { sent: () => number; restore: () => void };
+  return { restore: flag.restore, sentCount: flag.sent };
+}