test(e2e): Playwright photos-ready flow + visual evidence (#65)

Drive batch → pick calibration → Mask (Black) → Axis → Measure Calculate →
Photos ready against set1-48x2 fixtures on local vite preview. Capture
screenshots under tests/e2e/artifacts/; commit README + small evidence JPEGs.

frontend/package.json

@@ -7,13 +7,16 @@
     "dev": "vite",
     "build": "tsc --noEmit && vite build",
     "preview": "vite preview",
-    "test": "node --import tsx --test src/**/*.test.ts"
+    "test": "node --import tsx --test src/**/*.test.ts",
+    "test:e2e": "playwright test",
+    "test:e2e:headed": "playwright test --headed"
   },
   "dependencies": {
     "idb-keyval": "^6.3.0",
     "svelte": "^4.2.20"
   },
   "devDependencies": {
+    "@playwright/test": "^1.63.0",
     "@sveltejs/vite-plugin-svelte": "^3.1.2",
     "svelte-preprocess": "^5.1.4",
     "tsx": "^4.23.13",