Added Vitest to web/, ready for tests

web/vite.config.ts

@@ -1,3 +1,4 @@
+/// <reference types="vitest/config" />
 import tailwindcss from '@tailwindcss/vite';
 import { fileURLToPath } from 'node:url';
 import { defineConfig, loadEnv } from 'vite';
@@ -23,5 +24,12 @@ export default defineConfig(({ mode }) => {
         '/ws': { target, ws: true, changeOrigin: false },
       },
     },
+    // Vitest. vite-plugin-solid would run tests in jsdom, which isn't
+    // installed: nothing tested yet renders, and Solid's reactivity works
+    // in Node as it is. passWithNoTests until the first tests are added.
+    test: {
+      environment: 'node',
+      passWithNoTests: true,
+    },
   };
 });