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

dashboard/src/apiEvents.ts

@@ -32,8 +32,12 @@ export async function fetchEventById(eventId: string) {
   return data;
 }
 
-export async function deleteEvent(eventId: string) {
-  const res = await fetch(`/api/events/${encodeURIComponent(eventId)}`, {
+export async function deleteEvent(eventId: string, force: boolean = false) {
+  const url = force 
+    ? `/api/events/${encodeURIComponent(eventId)}?force=1`
+    : `/api/events/${encodeURIComponent(eventId)}`;
+  
+  const res = await fetch(url, {
     method: 'DELETE',
   });
   const data = await res.json();