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

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

public/style.css

@@ -92,6 +92,62 @@ nav {
 	background: rgba(91, 156, 246, 0.12);
 }
 
+/* ===== MAINTENANCE MENU ===== */
+
+.maint-menu {
+	margin-left: auto;
+	position: relative;
+}
+
+.maint-toggle {
+	background: none;
+	border: none;
+	color: var(--text-dim);
+	font-size: 1.2rem;
+	cursor: pointer;
+	padding: 0.3rem 0.5rem;
+	border-radius: 4px;
+	line-height: 1;
+	transition: color 0.1s, background 0.1s;
+}
+
+.maint-toggle:hover {
+	color: var(--text);
+	background: var(--surface-raised);
+}
+
+.maint-dropdown {
+	position: absolute;
+	right: 0;
+	top: calc(100% + 4px);
+	background: var(--surface);
+	border: 1px solid var(--border);
+	border-radius: 6px;
+	box-shadow: 0 4px 16px rgba(0,0,0,0.4);
+	min-width: 240px;
+	z-index: 200;
+	padding: 0.3rem;
+}
+
+.maint-item {
+	display: block;
+	width: 100%;
+	text-align: left;
+	background: none;
+	border: none;
+	color: var(--text);
+	font-family: inherit;
+	font-size: 0.9rem;
+	padding: 0.5rem 0.75rem;
+	cursor: pointer;
+	border-radius: 4px;
+	transition: background 0.1s;
+}
+
+.maint-item:hover {
+	background: var(--surface-raised);
+}
+
 /* ===== MAIN ===== */
 
 #main {