Fix single event deletion functionality with proper recurring vs non-recurring handling

This commit resolves multiple issues with event deletion:

Backend fixes:
- Fix CalDAV URL construction for DELETE requests (missing slash separator)
- Improve event lookup by href with exact matching and fallback to UID extraction
- Add support for both RFC3339 and simple YYYY-MM-DD date formats in occurrence parsing
- Implement proper logic to distinguish recurring vs non-recurring events in delete_this action
- For non-recurring events: delete entire event from CalDAV server
- For recurring events: add EXDATE to exclude specific occurrences
- Add comprehensive debug logging for troubleshooting deletion issues

Frontend fixes:
- Update callback signatures to support series endpoint parameters (7-parameter tuples)
- Add update_series method to CalendarService for series-specific operations
- Route single occurrence modifications through series endpoint with proper scoping
- Fix all component prop definitions to use new callback signature
- Update all emit calls to pass correct number of parameters

The deletion process now works correctly:
- Single events are completely removed from the calendar
- Recurring event occurrences are properly excluded via EXDATE
- Debug logging helps identify and resolve CalDAV communication issues

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

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

backend/src/calendar.rs

@@ -1015,7 +1015,7 @@ impl CalDAVClient {
             } else {
                 calendar_path
             };
-            format!("{}/dav.php{}{}", self.config.server_url.trim_end_matches('/'), clean_path, event_href)
+            format!("{}/dav.php{}/{}", self.config.server_url.trim_end_matches('/'), clean_path, event_href)
         };
         
         println!("Deleting event at: {}", full_url);