Add maintenance menu (top-right ⚙) with generate missing PDF thumbnails

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server.mjs

@@ -544,6 +544,25 @@ app.delete('/api/pdfs/:id', (req, res) => {
 	ok(res);
 });
 
+// ---------------------------------------------------------------------------
+// Maintenance
+// ---------------------------------------------------------------------------
+
+app.post('/api/maintenance/pdf-thumbs', (req, res) => {
+	const pdfs = list_pdfs();
+	let generated = 0;
+	for (const pdf of pdfs) {
+		if (pdf.thumb_filename) continue;
+		const thumb_prefix = join('./data/pdfs', pdf.id + '-thumb');
+		const thumb_file = generate_pdf_thumb(join('./data/pdfs', pdf.filename), thumb_prefix);
+		if (thumb_file) {
+			set_pdf({ ...pdf, thumb_filename: thumb_file });
+			generated++;
+		}
+	}
+	ok(res, { generated, total: pdfs.length });
+});
+
 // SPA fallback — serve index.html for any non-API, non-asset path
 const INDEX_HTML = new URL('./public/index.html', import.meta.url).pathname;
 app.get('/{*path}', (req, res) => res.sendFile(INDEX_HTML));