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/fixtures.ts

@@ -0,0 +1,99 @@
+import { type ChildProcess, spawn } from 'node:child_process';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import { test as base } from '@playwright/test';
+
+const REPO_ROOT = path.resolve(__dirname, '..');
+const BASE_PORT = 18100;
+
+export interface BackendFixture {
+  url: string;
+  dataDir: string;
+}
+
+async function waitForHealth(url: string, timeoutMs = 60_000): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    try {
+      const res = await fetch(`${url}/health`);
+      if (res.ok) return;
+    } catch {
+      // not up yet
+    }
+    await new Promise((resolve) => setTimeout(resolve, 500));
+  }
+  throw new Error(`backend at ${url} did not become healthy within ${timeoutMs}ms`);
+}
+
+export const test = base.extend<Record<never, never>, { backend: BackendFixture }>({
+  backend: [
+    async ({}, use, workerInfo) => {
+      const port = BASE_PORT + workerInfo.workerIndex;
+      const url = `http://127.0.0.1:${port}`;
+      // uvicorn resolves the data dir from cwd, so a temp cwd isolates
+      // each worker's SQLite and audio files completely.
+      const dataDir = mkdtempSync(path.join(tmpdir(), `voicebox-e2e-${workerInfo.workerIndex}-`));
+      const python = process.env.VOICEBOX_PYTHON ?? path.join(REPO_ROOT, '.venv-ci/bin/python');
+
+      const proc: ChildProcess = spawn(
+        python,
+        ['-m', 'uvicorn', 'backend.main:app', '--port', String(port), '--log-level', 'warning'],
+        {
+          cwd: dataDir,
+          env: {
+            ...process.env,
+            PYTHONPATH: REPO_ROOT,
+            VOICEBOX_FAKE_TTS: '1',
+            VOICEBOX_CORS_ORIGINS:
+              'http://localhost:4173,http://127.0.0.1:4173,http://localhost:5173',
+          },
+          stdio: ['ignore', 'pipe', 'pipe'],
+        },
+      );
+      const logs: Buffer[] = [];
+      proc.stdout?.on('data', (chunk) => logs.push(chunk));
+      proc.stderr?.on('data', (chunk) => logs.push(chunk));
+
+      try {
+        await waitForHealth(url);
+      } catch (error) {
+        proc.kill('SIGKILL');
+        throw new Error(`${(error as Error).message}\nbackend log:\n${Buffer.concat(logs)}`);
+      }
+
+      await use({ url, dataDir });
+
+      proc.kill('SIGTERM');
+      await new Promise((resolve) => {
+        proc.once('exit', resolve);
+        setTimeout(resolve, 5000);
+      });
+      rmSync(dataDir, { recursive: true, force: true });
+    },
+    { scope: 'worker' },
+  ],
+
+  // Point the app's persisted server store at this worker's backend before
+  // any page script runs.
+  page: async ({ page, backend }, use) => {
+    await page.addInitScript((serverUrl) => {
+      window.localStorage.setItem(
+        'voicebox-server',
+        JSON.stringify({
+          state: {
+            serverUrl,
+            isConnected: false,
+            mode: 'local',
+            keepServerRunningOnClose: false,
+            customModelsDir: null,
+          },
+          version: 0,
+        }),
+      );
+    }, backend.url);
+    await use(page);
+  },
+});
+
+export { expect } from '@playwright/test';