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/js/editor.js

@@ -16,6 +16,10 @@ class MarkdownEditor {
         this.editor = null; // Will be initialized later
         this.isShowingCustomPreview = false; // Flag to prevent auto-update when showing binary files
 
+        // Initialize loading spinners (will be created lazily when needed)
+        this.editorSpinner = null;
+        this.previewSpinner = null;
+
         // Only initialize CodeMirror if not in read-only mode (view mode)
         if (!readOnly) {
             this.initCodeMirror();
@@ -206,11 +210,34 @@ class MarkdownEditor {
         }
     }
 
+    /**
+     * Initialize loading spinners (lazy initialization)
+     */
+    initLoadingSpinners() {
+        if (!this.editorSpinner && !this.readOnly && this.editorElement) {
+            this.editorSpinner = new LoadingSpinner(this.editorElement, 'Loading file...');
+        }
+        if (!this.previewSpinner && this.previewElement) {
+            this.previewSpinner = new LoadingSpinner(this.previewElement, 'Rendering preview...');
+        }
+    }
+
     /**
      * Load file
      */
     async loadFile(path) {
         try {
+            // Initialize loading spinners if not already done
+            this.initLoadingSpinners();
+
+            // Show loading spinners
+            if (this.editorSpinner) {
+                this.editorSpinner.show('Loading file...');
+            }
+            if (this.previewSpinner) {
+                this.previewSpinner.show('Loading preview...');
+            }
+
             // Reset custom preview flag when loading text files
             this.isShowingCustomPreview = false;
 
@@ -232,8 +259,25 @@ class MarkdownEditor {
 
             // Save as last viewed page
             this.saveLastViewedPage(path);
+
+            // Hide loading spinners
+            if (this.editorSpinner) {
+                this.editorSpinner.hide();
+            }
+            if (this.previewSpinner) {
+                this.previewSpinner.hide();
+            }
+
             // No notification for successful file load - it's not critical
         } catch (error) {
+            // Hide loading spinners on error
+            if (this.editorSpinner) {
+                this.editorSpinner.hide();
+            }
+            if (this.previewSpinner) {
+                this.previewSpinner.hide();
+            }
+
             console.error('Failed to load file:', error);
             if (window.showNotification) {
                 window.showNotification('Failed to load file', 'danger');
@@ -409,6 +453,14 @@ class MarkdownEditor {
         }
 
         try {
+            // Initialize loading spinners if not already done
+            this.initLoadingSpinners();
+
+            // Show preview loading spinner (only if not already shown by loadFile)
+            if (this.previewSpinner && !this.previewSpinner.isVisible()) {
+                this.previewSpinner.show('Rendering preview...');
+            }
+
             // Step 0: Convert JSX-style syntax to HTML
             let processedContent = this.convertJSXToHTML(markdown);
 
@@ -422,6 +474,9 @@ class MarkdownEditor {
             if (!this.marked) {
                 console.error("Markdown parser (marked) not initialized.");
                 previewDiv.innerHTML = `<div class="alert alert-danger">Preview engine not loaded.</div>`;
+                if (this.previewSpinner) {
+                    this.previewSpinner.hide();
+                }
                 return;
             }
 
@@ -459,6 +514,13 @@ class MarkdownEditor {
                     console.warn('Mermaid rendering error:', error);
                 }
             }
+
+            // Hide preview loading spinner after a small delay to ensure rendering is complete
+            setTimeout(() => {
+                if (this.previewSpinner) {
+                    this.previewSpinner.hide();
+                }
+            }, 100);
         } catch (error) {
             console.error('Preview rendering error:', error);
             previewDiv.innerHTML = `
@@ -467,6 +529,11 @@ class MarkdownEditor {
                     ${error.message}
                 </div>
             `;
+
+            // Hide loading spinner on error
+            if (this.previewSpinner) {
+                this.previewSpinner.hide();
+            }
         }
     }