fix(client): downgrade vitest to ^3.x to align with vite@5

vitest@4 requires vite@^6, causing two conflicting esbuild versions in
the lockfile and EBADPLATFORM errors during Docker npm ci. Pin to vitest
3.x which supports vite@5 and resolves a single esbuild@0.21.5.

client/package.json

@@ -40,7 +40,7 @@
     "@types/react-dom": "^18.2.19",
     "@types/react-window": "^1.8.8",
     "@vitejs/plugin-react": "^4.2.1",
-    "@vitest/coverage-v8": "^4.1.2",
+    "@vitest/coverage-v8": "^3.2.4",
     "autoprefixer": "^10.4.18",
     "jsdom": "^29.0.1",
     "msw": "^2.13.0",
@@ -50,6 +50,6 @@
     "typescript": "^6.0.2",
     "vite": "^5.1.4",
     "vite-plugin-pwa": "^0.21.0",
-    "vitest": "^4.1.2"
+    "vitest": "^3.2.4"
   }
 }