Add site generation timestamp

frontend/src/App.svelte

@@ -60,4 +60,5 @@
 
   <CrateList crates={t_crates} filter={selected_crates} cols_shown={cols} />
 
+  <div>Page generated at: {BUILD_DATE}</div>
 </main>

frontend/src/vite-env.d.ts

@@ -1,2 +1,3 @@
 /// <reference types="svelte" />
 /// <reference types="vite/client" />
+declare const BUILD_DATE: string;

frontend/vite.config.ts

@@ -1,7 +1,10 @@
-import { defineConfig } from 'vite'
-import { svelte } from '@sveltejs/vite-plugin-svelte'
+import {defineConfig} from 'vite'
+import {svelte} from '@sveltejs/vite-plugin-svelte'
 
 // https://vitejs.dev/config/
 export default defineConfig({
-  plugins: [svelte()],
+    plugins: [svelte()],
+    define: {
+        BUILD_DATE: JSON.stringify(new Date().toISOString())
+    }
 })