test: Playwright E2E with real backend + fake TTS engine

e2e/ drives the web build (vite preview) against a per-worker uvicorn:
each Playwright worker boots its own backend on its own port with a
temp cwd, so SQLite and audio files are fully isolated and parallel-
safe. The page fixture seeds the persisted voicebox-server store with
the worker's URL before any script runs.

VOICEBOX_FAKE_TTS=1 short-circuits get_tts_backend_for_engine to a
backend that synthesizes a sine tone sized to the text — the real task
queue, SSE progress, history rows, and audio serving all run, only
inference is fake. backend/requirements-ci.txt is the slim dependency
set validated to boot the app on a CPU-only runner.

Specs: startup, settings layout, seeded profile in /voices, and
generate-to-completed-audio through the full pipeline.

e2e/helpers/api.ts

@@ -0,0 +1,58 @@
+/** Direct REST seeding against the per-worker backend — faster and less
+ *  brittle than driving every prerequisite through the UI. */
+
+export interface SeededProfile {
+  id: string;
+  name: string;
+}
+
+/** A 3-second 220 Hz sine WAV (backend requires samples >= 2s). */
+export function buildSampleWav(): Blob {
+  const sampleRate = 24_000;
+  const seconds = 3;
+  const samples = sampleRate * seconds;
+  const dataSize = samples * 2;
+  const buffer = new ArrayBuffer(44 + dataSize);
+  const view = new DataView(buffer);
+  const writeString = (offset: number, s: string) => {
+    for (let i = 0; i < s.length; i++) view.setUint8(offset + i, s.charCodeAt(i));
+  };
+  writeString(0, 'RIFF');
+  view.setUint32(4, 36 + dataSize, true);
+  writeString(8, 'WAVE');
+  writeString(12, 'fmt ');
+  view.setUint32(16, 16, true);
+  view.setUint16(20, 1, true);
+  view.setUint16(22, 1, true);
+  view.setUint32(24, sampleRate, true);
+  view.setUint32(28, sampleRate * 2, true);
+  view.setUint16(32, 2, true);
+  view.setUint16(34, 16, true);
+  writeString(36, 'data');
+  view.setUint32(40, dataSize, true);
+  for (let i = 0; i < samples; i++) {
+    view.setInt16(44 + i * 2, Math.round(0.1 * 32767 * Math.sin((2 * Math.PI * 220 * i) / sampleRate)), true);
+  }
+  return new Blob([buffer], { type: 'audio/wav' });
+}
+
+export async function seedProfile(backendUrl: string, name: string): Promise<SeededProfile> {
+  const createRes = await fetch(`${backendUrl}/profiles`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ name, language: 'en' }),
+  });
+  if (!createRes.ok) throw new Error(`create profile failed: ${createRes.status}`);
+  const profile = (await createRes.json()) as { id: string };
+
+  const form = new FormData();
+  form.append('file', buildSampleWav(), 'sample.wav');
+  form.append('reference_text', 'hello world this is a reference sample');
+  const sampleRes = await fetch(`${backendUrl}/profiles/${profile.id}/samples`, {
+    method: 'POST',
+    body: form,
+  });
+  if (!sampleRes.ok) throw new Error(`add sample failed: ${sampleRes.status} ${await sampleRes.text()}`);
+
+  return { id: profile.id, name };
+}