Add My Library for reusable assets (clip art, templates)

- Save layer or selection to personal library
- Browse library with category grouping and thumbnails
- Insert assets as new layers (double-click or Insert button)
- Delete unwanted assets
- Export library to JSON for backup
- Import library from JSON backup
- Assets stored in browser IndexedDB (persistent)
- Categories: General, Shapes, Borders, Icons, Templates, etc.

frontend/src/css/layout.css

@@ -563,6 +563,82 @@ IMPORTANT: any new icon should also must be added on /service-worker.js + its ve
 	color: var(--text-color);
 	cursor:pointer;
 }
+/* My Library browser */
+.library-browser{
+	max-height: 400px;
+	overflow-y: auto;
+	padding: 10px;
+}
+.library-category{
+	margin-bottom: 20px;
+}
+.library-category h3{
+	margin: 0 0 10px 0;
+	padding-bottom: 5px;
+	border-bottom: 1px solid var(--border-color);
+	color: var(--text-color);
+	font-size: 14px;
+}
+.library-items{
+	display: flex;
+	flex-wrap: wrap;
+	gap: 10px;
+}
+.library-item{
+	width: 120px;
+	padding: 8px;
+	background: var(--area-background-color);
+	border: 1px solid var(--border-color);
+	border-radius: 4px;
+	cursor: pointer;
+	transition: 0.2s;
+}
+.library-item:hover{
+	border-color: var(--background-color-active);
+	transform: scale(1.02);
+}
+.library-item img{
+	width: 100%;
+	height: 80px;
+	object-fit: contain;
+	background: repeating-conic-gradient(#808080 0% 25%, #666 0% 50%) 50% / 10px 10px;
+	border-radius: 2px;
+}
+.library-item-name{
+	margin-top: 5px;
+	font-size: 11px;
+	color: var(--text-color);
+	text-align: center;
+	white-space: nowrap;
+	overflow: hidden;
+	text-overflow: ellipsis;
+}
+.library-item-actions{
+	display: flex;
+	gap: 5px;
+	margin-top: 5px;
+}
+.library-item-actions button{
+	flex: 1;
+	padding: 3px 5px;
+	font-size: 10px;
+	cursor: pointer;
+	border: 1px solid var(--border-color);
+	border-radius: 3px;
+	background: var(--section-background-color);
+	color: var(--text-color);
+}
+.library-item-actions .insert-btn{
+	background: var(--background-color-active);
+	color: var(--text-color-active);
+}
+.library-item-actions .delete-btn:hover{
+	background: #dc3545;
+	color: #fff;
+}
+.library-dialog .dialog_content{
+	min-width: 500px;
+}
 .sidebar_right .label{
 	display: inline-block;
 }