Add initial VibeGuard browser extension

src/background/offscreen.ts

@@ -0,0 +1,15 @@
+import type { RuntimeMessage } from "../shared/types";
+
+const worker = new Worker(chrome.runtime.getURL("inference.js"), { type: "module" });
+
+chrome.runtime.onMessage.addListener((message: RuntimeMessage, _sender, sendResponse) => {
+  if (message.type !== "OFFSCREEN_INFER") return false;
+  const listener = (event: MessageEvent<{ results?: unknown; error?: string }>) => {
+    worker.removeEventListener("message", listener);
+    if (event.data.error) sendResponse({ error: event.data.error });
+    else sendResponse({ results: event.data.results });
+  };
+  worker.addEventListener("message", listener);
+  worker.postMessage({ requests: message.requests });
+  return true;
+});