add offline support

src/services/offline-manifest.js

@@ -0,0 +1,20 @@
+import fs from 'node:fs';
+import path from 'node:path';
+
+/** Only the app shell; route data is downloaded separately on explicit request. */
+export function offlineManifest(publicDirectory) {
+  const resources = new Set(['/']);
+  const appDirectories = new Set(['css', 'js', 'vendor', 'assets', 'images']);
+  function visit(directory, prefix = '') {
+    for (const entry of fs.readdirSync(directory, { withFileTypes: true })) {
+      if (entry.name.startsWith('.')) continue;
+      if (!prefix && entry.isDirectory() && !appDirectories.has(entry.name)) continue;
+      if (prefix === '/images' && entry.isDirectory() && !['icons', 'group-symbols'].includes(entry.name)) continue;
+      const relative = `${prefix}/${encodeURIComponent(entry.name)}`;
+      if (entry.isDirectory()) visit(path.join(directory, entry.name), relative);
+      else if (entry.isFile() && /\.(?:html|css|js|svg|png|webp|jpg|jpeg|gif|ico|woff2?)$/i.test(entry.name)) resources.add(relative);
+    }
+  }
+  visit(publicDirectory);
+  return { resources: [...resources].sort() };
+}