feat: add testing framework and initial test cases

- Updated package.json to include Vitest and testing dependencies.
- Created test cases for SuitePicker component to validate selection logic.
- Added tests for ReportsPage to ensure correct report grouping and ordering.
- Implemented read-only enforcement tests for SuitePage to prevent actions on built-in suites.
- Introduced a setup file for Vitest to include jest-dom matchers and cleanup after tests.
- Modified ReportsPage to group reports by model and display them accordingly.
- Enhanced API types to include suite_scope and question_count for better report handling.

web/vite.config.ts

@@ -1,4 +1,6 @@
-import { defineConfig } from 'vite'
+// defineConfig comes from vitest/config rather than vite so the `test` block
+// below type-checks; it is vite's own, widened with Vitest's options.
+import { defineConfig } from 'vitest/config'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
 
@@ -28,4 +30,11 @@ export default defineConfig({
     emptyOutDir: true,
     chunkSizeWarningLimit: 900,
   },
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./src/test/setup.ts'],
+    // Only our own tests; node_modules and the built bundle are not ours.
+    include: ['src/**/*.test.{ts,tsx}'],
+  },
 })