ci: enforce 80% backend coverage gate and add frontend coverage reporting

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -12,6 +12,7 @@
     "lint": "eslint .",
     "preview": "vite preview",
     "test": "vitest run",
+    "test:coverage": "vitest run --coverage",
     "test:watch": "vitest",
     "test:e2e": "playwright test",
     "test:e2e:headed": "playwright test --headed",
@@ -48,6 +49,7 @@
     "recharts": "^3.7.0",
     "sonner": "^2.0.7",
     "tailwind-merge": "^3.4.0",
+    "web-vitals": "^4.2.4",
     "zundo": "^2.3.0",
     "zustand": "^5.0.10"
   },
@@ -60,6 +62,7 @@
     "@types/node": "^24.10.9",
     "@types/react": "^19.2.5",
     "@types/react-dom": "^19.2.3",
+    "@vitest/coverage-v8": "^4.0.18",
     "@vitejs/plugin-react": "^5.1.1",
     "eslint": "^9.39.1",
     "eslint-plugin-react-hooks": "^7.0.1",