Implement complete recurring event drag modification system

- Add recurring edit modal with three modification options:
  • "Only this event" - Creates exception for single occurrence
  • "This and future events" - Splits series from occurrence forward
  • "All occurrences in this series" - Updates entire series time

- Enhance backend update API to support series modifications:
  • Add update_action parameter for recurring event operations
  • Implement time-only updates that preserve original start dates
  • Convert timestamped occurrence UIDs to base UIDs for series updates
  • Preserve recurrence rules during series modifications

- Fix recurring event drag operations:
  • Show modal for recurring events instead of direct updates
  • Handle EXDATE creation for single occurrence modifications
  • Support series splitting with UNTIL clause modifications
  • Maintain proper UID management for different modification types

- Clean up debug logging and restore page refresh for data consistency

🤖 Generated with [Claude Code](https://claude.ai/code)

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

styles.css

@@ -642,7 +642,7 @@ body {
 
 /* Week Events */
 .week-event {
-    position: absolute;
+    position: absolute !important;
     left: 4px;
     right: 4px;
     min-height: 20px;
@@ -1831,4 +1831,69 @@ body {
         min-width: 2.5rem;
         padding: 0.4rem 0.6rem;
     }
+}
+
+/* Recurring Edit Modal */
+.recurring-edit-modal {
+    max-width: 500px;
+    width: 95%;
+}
+
+.recurring-edit-options {
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+    margin: 1.5rem 0;
+}
+
+.recurring-option {
+    background: white;
+    border: 2px solid #e9ecef;
+    color: #495057;
+    padding: 1rem;
+    text-align: left;
+    border-radius: 8px;
+    cursor: pointer;
+    transition: all 0.2s ease;
+}
+
+.recurring-option:hover {
+    border-color: #667eea;
+    background: #f8f9ff;
+    color: #495057;
+    transform: none;
+    box-shadow: 0 2px 8px rgba(102, 126, 234, 0.15);
+}
+
+.recurring-option .option-title {
+    font-size: 1rem;
+    font-weight: 600;
+    margin-bottom: 0.5rem;
+    color: #333;
+}
+
+.recurring-option .option-description {
+    font-size: 0.9rem;
+    color: #666;
+    line-height: 1.4;
+}
+
+/* Mobile adjustments for recurring edit modal */
+@media (max-width: 768px) {
+    .recurring-edit-modal {
+        margin: 1rem;
+        width: calc(100% - 2rem);
+    }
+    
+    .recurring-option {
+        padding: 0.75rem;
+    }
+    
+    .recurring-option .option-title {
+        font-size: 0.9rem;
+    }
+    
+    .recurring-option .option-description {
+        font-size: 0.8rem;
+    }
 }