Merge feat/longform-pipeline: VAD long-form pipeline, opt-in (spec 001 workstream 3)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

# Conflicts:
#	docs/Architecture.md
#	docs/Decisions.md
#	src/App.tsx
#	src/index.css
#	src/lib/engine.ts
#	src/worker/inference.worker.ts
#	src/worker/protocol.ts
#	tests/engine.test.ts
#	tests/live-real-model.test.ts
#	tests/offline.md
#	tests/protocol.test.ts

tests/engine.test.ts

@@ -88,6 +88,15 @@ describe("BrowserEngine", () => {
     expect("prompt" in worker.posted[2]!.message).toBe(false);
   });
 
+  test("forwards the long-form request only when set (D-WS3a)", () => {
+    const worker = new FakeWorker();
+    const engine = new BrowserEngine(worker);
+    void engine.transcribe(new Float32Array(4), { longForm: true });
+    void engine.transcribe(new Float32Array(4));
+    expect(worker.posted[0]!.message.longForm).toBe(true);
+    expect("longForm" in worker.posted[1]!.message).toBe(false);
+  });
+
   test("asks the worker to stream only when a consumer listens", () => {
     const worker = new FakeWorker();
     const engine = new BrowserEngine(worker);