Implement drag-to-move functionality for events in week view with CalDAV server integration

- Add drag-to-move event handlers to existing events in week view
- Extend drag state management to support both create and move operations
- Implement visual feedback with event preview during drag and hidden original
- Calculate new start/end times while preserving event duration
- Add CalDAV server update integration via calendar service
- Wire event update callbacks through component hierarchy (WeekView → Calendar → RouteHandler → App)
- Preserve all original event properties (title, description, location, reminders, etc.)
- Handle timezone conversion from local to UTC for server storage
- Add error handling with user feedback and success confirmation
- Include moving event CSS styling with enhanced visual feedback

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

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

styles.css

@@ -696,6 +696,37 @@ body {
     user-select: none;
 }
 
+/* Moving event during drag */
+.temp-event-box.moving-event {
+    background: inherit; /* Use the event's actual color */
+    border: 2px solid rgba(255, 255, 255, 0.8);
+    color: white;
+    flex-direction: column;
+    align-items: flex-start;
+    justify-content: flex-start;
+    text-align: left;
+    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.3);
+    transform: scale(1.02);
+}
+
+.temp-event-box.moving-event .event-title {
+    font-weight: 600;
+    margin-bottom: 2px;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+    width: 100%;
+}
+
+.temp-event-box.moving-event .event-time {
+    font-size: 0.65rem;
+    opacity: 0.9;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+    width: 100%;
+}
+
 .week-event .event-title {
     font-weight: 600;
     margin-bottom: 2px;