ci: add minimal frontend tests, backend coverage tooling, and fix mypy

frontend/package.json

@@ -7,6 +7,8 @@
     "build": "next build",
     "start": "next start",
     "lint": "eslint",
+    "test": "vitest run --passWithNoTests --coverage",
+    "test:watch": "vitest",
     "dev:lan": "next dev --hostname 0.0.0.0 --port 3000",
     "api:gen": "orval --config ./orval.config.ts"
   },
@@ -29,14 +31,19 @@
     "remark-gfm": "^4.0.1"
   },
   "devDependencies": {
+    "@testing-library/jest-dom": "^6.6.3",
+    "@testing-library/react": "^16.1.0",
+    "@testing-library/user-event": "^14.5.2",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "@vitest/coverage-v8": "^2.1.8",
     "autoprefixer": "^10.4.24",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "eslint": "^9",
     "eslint-config-next": "16.1.6",
+    "jsdom": "^25.0.1",
     "lucide-react": "^0.563.0",
     "orval": "^8.2.0",
     "postcss": "^8.5.6",
@@ -44,6 +51,7 @@
     "tailwind-merge": "^3.4.0",
     "tailwindcss": "^3.4.17",
     "tailwindcss-animate": "^1.0.7",
-    "typescript": "^5"
+    "typescript": "^5",
+    "vitest": "^2.1.8"
   }
 }