Fix series RRULE updates: editing 'all events' now properly updates original series RRULE

- Backend now updates RRULE when recurrence_count or recurrence_end_date parameters are provided
- Fixed update_entire_series() to modify COUNT/UNTIL instead of preserving original RRULE
- Added comprehensive RRULE parsing functions to extract existing frequency, interval, count, until, and BYDAY components
- Fixed frontend parameter mapping to pass recurrence parameters through update_series calls
- Resolves issue where changing recurring event from 5 to 7 occurrences kept original COUNT=5

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

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

backend/src/handlers/series.rs

@@ -262,8 +262,8 @@ pub async fn update_event_series(
     Json(request): Json<UpdateEventSeriesRequest>,
 ) -> Result<Json<UpdateEventSeriesResponse>, ApiError> {
     println!(
-        "🔄 Update event series request received: series_uid='{}', update_scope='{}'",
-        request.series_uid, request.update_scope
+        "🔄 Update event series request received: series_uid='{}', update_scope='{}', recurrence_count={:?}, recurrence_end_date={:?}",
+        request.series_uid, request.update_scope, request.recurrence_count, request.recurrence_end_date
     );
 
     // Extract and verify token
@@ -765,9 +765,36 @@ fn update_entire_series(
     updated_event.last_modified = Some(now);
     // Keep original created timestamp to preserve event history
 
-    // For simple updates (like drag operations), preserve the existing RRULE
-    // For more complex updates, we might need to regenerate it, but for now keep it simple
-    // updated_event.rrule remains unchanged from the clone
+    // Update RRULE if recurrence parameters are provided
+    if let Some(ref existing_rrule) = updated_event.rrule {
+        let mut new_rrule = existing_rrule.clone();
+        println!("🔄 Original RRULE: {}", existing_rrule);
+        
+        // Update COUNT if provided
+        if let Some(count) = request.recurrence_count {
+            println!("🔄 Updating RRULE with new COUNT: {}", count);
+            // Remove old COUNT or UNTIL parameters
+            new_rrule = new_rrule.split(';')
+                .filter(|part| !part.starts_with("COUNT=") && !part.starts_with("UNTIL="))
+                .collect::<Vec<_>>()
+                .join(";");
+            // Add new COUNT
+            new_rrule = format!("{};COUNT={}", new_rrule, count);
+        } else if let Some(ref end_date) = request.recurrence_end_date {
+            println!("🔄 Updating RRULE with new UNTIL: {}", end_date);
+            // Remove old COUNT or UNTIL parameters
+            new_rrule = new_rrule.split(';')
+                .filter(|part| !part.starts_with("COUNT=") && !part.starts_with("UNTIL="))
+                .collect::<Vec<_>>()
+                .join(";");
+            // Add new UNTIL (convert YYYY-MM-DD to YYYYMMDD format)
+            let until_date = end_date.replace("-", "");
+            new_rrule = format!("{};UNTIL={}", new_rrule, until_date);
+        }
+        
+        println!("🔄 Updated RRULE: {}", new_rrule);
+        updated_event.rrule = Some(new_rrule);
+    }
 
     // Copy the updated event back to existing_event for the main handler
     *existing_event = updated_event.clone();