Added tests for format and storage, run in UK time

web/vite.config.ts

@@ -26,9 +26,11 @@ export default defineConfig(({ mode }) => {
     },
     // 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.
+    // in Node as it is. Dates are shown in local time, so tests run in UK
+    // time wherever they run.
     test: {
       environment: 'node',
+      env: { TZ: 'Europe/London' },
     },
   };
 });