feat: Enhance WebDAV file management and UI

- Add functionality to create new collections via API
- Implement copy and move operations between collections
- Improve image rendering in markdown preview with relative path resolution
- Add support for previewing binary files (images, PDFs)
- Refactor modal styling to use flat buttons and improve accessibility

static/css/components.css

@@ -143,6 +143,15 @@ body.dark-mode .context-menu {
     animation: slideIn 0.3s ease;
 }
 
+/* Override Bootstrap warning background to be darker for better text contrast */
+.toast.bg-warning {
+    background-color: #cc9a06 !important;
+}
+
+body.dark-mode .toast.bg-warning {
+    background-color: #b8860b !important;
+}
+
 @keyframes slideIn {
     from {
         transform: translateX(400px);
@@ -276,4 +285,83 @@ body.dark-mode .modal-footer {
     color: var(--text-secondary);
     line-height: 1.4;
     margin-top: 8px;
+}
+
+/* Flat Button Styles */
+.btn-flat {
+    border: none;
+    border-radius: 0;
+    padding: 6px 12px;
+    font-size: 14px;
+    font-weight: 500;
+    transition: all 0.2s ease;
+    background-color: transparent;
+    color: var(--text-primary);
+    position: relative;
+}
+
+.btn-flat:hover {
+    background-color: var(--bg-tertiary);
+}
+
+.btn-flat:active {
+    transform: scale(0.95);
+}
+
+/* Flat button variants */
+.btn-flat-primary {
+    color: #0d6efd;
+}
+
+.btn-flat-primary:hover {
+    background-color: rgba(13, 110, 253, 0.1);
+}
+
+.btn-flat-success {
+    color: #198754;
+}
+
+.btn-flat-success:hover {
+    background-color: rgba(25, 135, 84, 0.1);
+}
+
+.btn-flat-danger {
+    color: #dc3545;
+}
+
+.btn-flat-danger:hover {
+    background-color: rgba(220, 53, 69, 0.1);
+}
+
+.btn-flat-warning {
+    color: #ffc107;
+}
+
+.btn-flat-warning:hover {
+    background-color: rgba(255, 193, 7, 0.1);
+}
+
+.btn-flat-secondary {
+    color: var(--text-secondary);
+}
+
+.btn-flat-secondary:hover {
+    background-color: var(--bg-tertiary);
+}
+
+/* Dark mode adjustments */
+body.dark-mode .btn-flat-primary {
+    color: #6ea8fe;
+}
+
+body.dark-mode .btn-flat-success {
+    color: #75b798;
+}
+
+body.dark-mode .btn-flat-danger {
+    color: #ea868f;
+}
+
+body.dark-mode .btn-flat-warning {
+    color: #ffda6a;
 }