Implement side-by-side rendering for overlapping events in week view

- Add overlap detection algorithm to identify overlapping events
- Implement layout calculation to arrange events in columns
- Update event positioning to use dynamic left/width instead of fixed right
- Events now render side-by-side when they overlap in time
- Maintains proper spacing and margins for all event arrangements

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

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

frontend/styles.css

@@ -782,8 +782,7 @@ body {
 /* Week Events */
 .week-event {
     position: absolute !important;
-    left: 4px;
-    right: 4px;
+    /* left and width are now set inline for overlap handling */
     min-height: 20px;
     background: #3B82F6;
     color: white;