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.

bun.lock

@@ -10,6 +10,7 @@
       },
       "devDependencies": {
         "@biomejs/biome": "2.3.12",
+        "@playwright/test": "^1.62.1",
         "@types/node": "^20.0.0",
         "@vitejs/plugin-react": "^6.0.5",
         "@vitest/browser": "^4.1.10",
@@ -304,6 +305,8 @@
 
     "@oxc-project/types": ["@oxc-project/[email protected]", "", {}, "sha512-u6JZdLBTLotrNC9Vd6vPssINdzcCzleKAH6EJKImQb7GtYvX5keN2dxkoK44stCc4tffE6QQRtZTXVSzsLUlWA=="],
 
+    "@playwright/test": ["@playwright/[email protected]", "", { "dependencies": { "playwright": "1.62.1" }, "bin": { "playwright": "cli.js" } }, "sha512-DTcUc8qii+cpHvtOwggMtBRMjKZHXYWdw8syRYu2vtzuq4Wxphqq4NfCs5Zt44L6mA8rfDfj+PHnxFc/FeK6mQ=="],
+
     "@polka/url": ["@polka/[email protected]", "", {}, "sha512-wwQAWhWSuHaag8c4q/KN/vCoeOJYshAIvMQwD4GpSb3OiZklFfvAgmj0VCBBImRpuF/aFgIRzllXlVX93Jevww=="],
 
     "@radix-ui/number": ["@radix-ui/[email protected]", "", {}, "sha512-MkKCwxlXTgz6CFoJx3pCwn07GKp36+aZyu/u2Ln2VrA5DcdyCZkASEDBTd8x5whTQQL5CiYf4prXKLcgQdv29g=="],