docs: clarify event deletion flows and dialog handling for all event types

- Documented unified deletion process for single, single-in-series, and recurring series events
- Explained custom dialog interception of Syncfusion RecurrenceAlert and DeleteAlert
- Updated both README.md and .github/copilot-instructions.md to match current frontend logic

README.md

@@ -39,7 +39,7 @@ A comprehensive multi-service digital signage solution for educational instituti
 
 ## 🌟 Key Features
 
-### 📊 **Dashboard Management**
+
 - Modern React-based web interface with Syncfusion components
 - Real-time client monitoring and group management
 - Event scheduling with academic period support
@@ -47,13 +47,19 @@ A comprehensive multi-service digital signage solution for educational instituti
 - Holiday calendar integration
  - Visual indicators: TentTree icon next to the main event icon marks events that skip holidays (icon color: black)
 
+- **Event Deletion**: All event types (single, single-in-series, entire series) are handled with custom dialogs. The frontend intercepts Syncfusion's built-in RecurrenceAlert and DeleteAlert popups to provide a unified, user-friendly deletion flow:
+   - Single (non-recurring) event: deleted directly after confirmation.
+   - Single occurrence of a recurring series: user can delete just that instance.
+   - Entire recurring series: user can delete all occurrences after a final custom confirmation dialog.
+   - Detached occurrences (edited/broken out): treated as single events.
+
 ### 🎯 **Event System**
 - **Presentations**: PowerPoint/LibreOffice → PDF conversion via Gotenberg
 - **Websites**: URL-based content display
 - **Videos**: Media file streaming
 - **Messages**: Text announcements
 - **WebUntis**: Educational schedule integration
- - **Recurrence & Holidays**: Recurring events can be configured to skip holidays. The backend generates EXDATEs (RecurrenceException) for holiday occurrences so the calendar never shows those instances. The "Termine an Ferientagen erlauben" toggle does not affect these events.
+ - **Recurrence & Holidays**: Recurring events can be configured to skip holidays. The backend generates EXDATEs (RecurrenceException) for holiday occurrences using RFC 5545 timestamps (yyyyMMddTHHmmssZ), so the calendar never shows those instances. The "Termine an Ferientagen erlauben" toggle does not affect these events.
 - **Single Occurrence Editing**: Users can edit individual occurrences of recurring events without affecting the master series. The system provides a confirmation dialog to choose between editing a single occurrence or the entire series.
 
 ### 🏫 **Academic Period Management**
@@ -278,10 +284,11 @@ mosquitto_sub -h localhost -t "infoscreen/+/heartbeat" -v
 ## 🎨 Frontend Features
 
 ### Recurrence & holidays
-- The frontend manually expands recurring events due to Syncfusion EXDATE handling limitations.
-- The API supplies `RecurrenceException` (EXDATE) with exact occurrence start times (UTC) so holiday instances are excluded.
-- Events with "skip holidays" display a TentTree icon next to the main event icon.
-- Single occurrence editing: Users can detach individual occurrences via confirmation dialog, creating standalone events while preserving the master series.
+- Recurrence is handled natively by Syncfusion. The API returns master events with `RecurrenceRule` and `RecurrenceException` (EXDATE) in RFC 5545 format (yyyyMMddTHHmmssZ, UTC) so the Scheduler excludes holiday instances reliably.
+- Events with "skip holidays" display a TentTree icon next to the main event icon (icon color: black). The Scheduler’s native lower-right recurrence badge indicates series membership.
+- Single occurrence editing: Users can edit either a single occurrence or the entire series. The UI persists changes using `onActionCompleted (requestType='eventChanged')`:
+   - Single occurrence → `POST /api/events/<id>/occurrences/<date>/detach` (creates standalone event and adds EXDATE to master)
+   - Series/single event → `PUT /api/events/<id>`
 
 ### Syncfusion Components Used (Material 3)
 - **Schedule**: Event calendar with drag-drop support