feat(events): reliable holiday skipping for recurrences + UI badge; clean logs

Backend: generate EventException on create/update when skip_holidays or recurrence changes; emit RecurrenceException (EXDATE) with exact occurrence start time (UTC)
API: return master events with RecurrenceRule + RecurrenceException
Frontend: map RecurrenceException → recurrenceException; ensure SkipHolidays instances never render on holidays; place TentTree icon (black) next to main event icon via template
Docs: update README and Copilot instructions for recurrence/holiday behavior
Cleanup: remove dataSource and debug console logs

dashboard/src/apiEventExceptions.ts

@@ -0,0 +1,31 @@
+export interface EventException {
+  id?: number;
+  event_id: number;
+  exception_date: string; // YYYY-MM-DD
+  is_skipped: boolean;
+  override_title?: string;
+  override_description?: string;
+  override_start?: string;
+  override_end?: string;
+}
+
+export async function createEventException(exception: Omit<EventException, 'id'>) {
+  const res = await fetch('/api/event_exceptions', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(exception),
+  });
+  const data = await res.json();
+  if (!res.ok || data.error) throw new Error(data.error || 'Fehler beim Erstellen der Ausnahme');
+  return data;
+}
+
+export async function listEventExceptions(eventId?: number) {
+  const params = new URLSearchParams();
+  if (eventId) params.set('event_id', eventId.toString());
+  
+  const res = await fetch(`/api/event_exceptions?${params.toString()}`);
+  const data = await res.json();
+  if (!res.ok || data.error) throw new Error(data.error || 'Fehler beim Laden der Ausnahmen');
+  return data as EventException[];
+}