feat: Implement collection deletion and loading spinners

- Add API endpoint and handler to delete collections
- Introduce LoadingSpinner component for async operations
- Show loading spinners during file loading and preview rendering
- Enhance modal accessibility by removing aria-hidden attribute
- Refactor delete functionality to distinguish between collections and files/folders
- Remove unused collection definitions from config

static/css/components.css

@@ -388,4 +388,66 @@ body.dark-mode #darkModeBtn i {
 #darkModeBtn:hover i {
     color: inherit;
     /* Inherit hover color from parent */
+}
+
+/* ===================================
+   Loading Spinner Component
+   =================================== */
+
+/* Loading overlay - covers the target container */
+.loading-overlay {
+    position: absolute;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    background: var(--bg-primary);
+    opacity: 0.95;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 1000;
+    transition: opacity 0.2s ease;
+}
+
+/* Loading spinner */
+.loading-spinner {
+    width: 48px;
+    height: 48px;
+    border: 4px solid var(--border-color);
+    border-top-color: var(--primary-color);
+    border-radius: 50%;
+    animation: spin 0.8s linear infinite;
+}
+
+/* Spinner animation */
+@keyframes spin {
+    to {
+        transform: rotate(360deg);
+    }
+}
+
+/* Loading text */
+.loading-text {
+    margin-top: 16px;
+    color: var(--text-secondary);
+    font-size: 14px;
+    text-align: center;
+}
+
+/* Loading container with spinner and text */
+.loading-content {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 12px;
+}
+
+/* Hide loading overlay by default */
+.loading-overlay.hidden {
+    display: none;
+}
+
+.language-bash {
+    color: var(--text-primary) !important;
 }