chore: add test infrastructure and update risk router

- Add vitest config and unit tests for components, api, stores
- Add Playwright e2e test for user flows
- Add backend test files
- Update risk.py with LOD grid KDTree optimization

frontend/vitest.config.ts

@@ -0,0 +1,19 @@
+/// <reference types="vitest" />
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+import path from 'path';
+
+export default defineConfig({
+  plugins: [react()],
+  resolve: {
+    alias: {
+      '@': path.resolve(__dirname, 'src'),
+    },
+  },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: [],
+    include: ['src/**/*.test.{ts,tsx}'],
+  },
+});