test(security): add scan comparison coverage (#656)

Backend supertest suite for GET /api/security/compare covers tier gating,
input validation, cross-node isolation, diff partitioning by
vulnerability_id::pkg_name, suppression application, and cross-image
comparison. Frontend vitest + React Testing Library scaffolding with
component tests for ScanComparisonSheet (loading, error recovery,
cross-image warning, filter pills, reload on id change) and
SecurityHistoryView (mount fetch, selection cap, oldest-first baseline
ordering, tier gating).

frontend/package.json

@@ -8,7 +8,9 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@dagrejs/dagre": "^3.0.0",
@@ -60,6 +62,10 @@
   "devDependencies": {
     "@eslint/js": "^10.0.1",
     "@tailwindcss/vite": "^4.2.2",
+    "@testing-library/dom": "^10.4.1",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@testing-library/user-event": "^14.6.1",
     "@types/node": "^25.5.2",
     "@types/react": "^19.2.7",
     "@types/react-dom": "^19.2.3",
@@ -68,9 +74,11 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.5.2",
     "globals": "^17.4.0",
+    "jsdom": "^29.0.2",
     "tailwindcss": "^4.2.2",
     "typescript": "^6.0.2",
     "typescript-eslint": "^8.58.1",
-    "vite": "^8.0.8"
+    "vite": "^8.0.8",
+    "vitest": "^4.1.4"
   }
 }