feat: 'Vor dem Kopieren bearbeiten' Checkbox im Kopieren-Popup

Über der Kalenderliste im Kopieren-Menü gibt es jetzt eine Checkbox
'Vor dem Kopieren bearbeiten'. Wenn aktiviert und ein Ziel-Kalender
geklickt wird, öffnet sich der Termin-erstellen-Dialog mit allen
Daten des Quell-Termins vorausgefüllt (Titel, Datum, Ort, Beschreibung,
Farbe, Wiederholung) und dem Ziel-Kalender vorausgewählt.

frontend/css/app.css

@@ -846,6 +846,15 @@ a { color: var(--primary); text-decoration: none; }
 }
 .popup-copy-item:hover { background: var(--bg-hover); }
 .popup-copy-dot { width: 10px; height: 10px; border-radius: 50%; flex-shrink: 0; }
+.popup-copy-edit-toggle {
+  display: flex; align-items: center; gap: 8px;
+  padding: 6px 14px 8px;
+  font-size: 12px; color: var(--text-2);
+  cursor: pointer;
+  border-bottom: 1px solid var(--border);
+  margin-bottom: 4px;
+}
+.popup-copy-edit-toggle input[type="checkbox"] { margin: 0; cursor: pointer; }
 
 /* ── Settings Page ──────────────────────────────────────── */
 #modal-settings.modal-overlay {

frontend/js/calendar.js

@@ -1027,7 +1027,12 @@ function showEventPopup(ev, anchor) {
     if (!menu.classList.contains('hidden')) { menu.classList.add('hidden'); return; }
     const targets = buildWritableCalendars(ev);
     if (!targets.length) { showToast('Keine Zielkalender verfügbar', true); return; }
-    menu.innerHTML = `<div class="popup-copy-label">${t('copy_to_calendar')}</div>` +
+    menu.innerHTML =
+      `<div class="popup-copy-label">${t('copy_to_calendar')}</div>` +
+      `<label class="popup-copy-edit-toggle">
+         <input type="checkbox" id="popup-copy-edit-cb" />
+         <span>${t('edit_before_copy')}</span>
+       </label>` +
       targets.map(c =>
         `<div class="popup-copy-item" data-cal-idx="${c._idx}">
           <span class="popup-copy-dot" style="background:${c.color}"></span>
@@ -1035,13 +1040,22 @@ function showEventPopup(ev, anchor) {
         </div>`
       ).join('');
     menu.classList.remove('hidden');
+
+    // Stop clicks on the checkbox label from closing the menu
+    menu.querySelector('.popup-copy-edit-toggle').addEventListener('click', e2 => e2.stopPropagation());
+
     menu.querySelectorAll('.popup-copy-item').forEach(el => {
       el.addEventListener('click', async ev2 => {
         ev2.stopPropagation();
+        const editFirst = document.getElementById('popup-copy-edit-cb').checked;
         menu.classList.add('hidden');
         popup.classList.add('hidden');
         const cal = targets[parseInt(el.dataset.calIdx)];
-        await copyEventToCalendar(ev, cal);
+        if (editFirst) {
+          openCopyEditModal(ev, cal);
+        } else {
+          await copyEventToCalendar(ev, cal);
+        }
       });
     });
   };
@@ -1149,6 +1163,43 @@ function openNewEventModal(date) {
   openModal('modal-event');
 }
 
+// Open the create-event modal pre-filled with an existing event's data, so
+// the user can edit before copying it into the target calendar.
+function openCopyEditModal(ev, targetCal) {
+  state.editingEvent = null;
+  state.selectedEventColor = ev.color || '';
+
+  document.getElementById('modal-event-title-label').textContent = 'Termin erstellen';
+  document.getElementById('ev-title').value       = ev.title || '';
+  document.getElementById('ev-location').value    = ev.location || '';
+  document.getElementById('ev-description').value = ev.description || '';
+  document.getElementById('ev-allday').checked    = !!ev.allDay;
+
+  if (ev.allDay) {
+    setDtValue('ev-start-date', (ev.start || '').slice(0, 10), 'date');
+    setDtValue('ev-end-date',   (ev.end   || '').slice(0, 10), 'date');
+  } else {
+    const s = new Date(ev.start);
+    const e = new Date(ev.end);
+    setDtValue('ev-start', toLocalDatetimeInput(s), 'datetime');
+    setDtValue('ev-end',   toLocalDatetimeInput(e), 'datetime');
+  }
+
+  toggleAlldayFields(!!ev.allDay);
+
+  // Map target calendar to the dropdown's option value
+  let selectedId;
+  if (targetCal.type === 'caldav') selectedId = targetCal.id;
+  else                              selectedId = `${targetCal.type}-${targetCal.id}`;
+  populateCalendarSelect(selectedId);
+
+  resetColorPicker(ev.color || '');
+  resetRecurrenceUI();
+  if (ev.rrule) parseRruleIntoUI(ev.rrule);
+  document.getElementById('ev-delete').classList.add('hidden');
+  openModal('modal-event');
+}
+
 function openEditEventModal(ev) {
   if (ev.source === 'ical') { showToast(t('event_readonly'), true); return; }
   state.editingEvent = ev;

frontend/js/i18n.js

@@ -153,6 +153,7 @@ const translations = {
     rec_ends: 'Endet', rec_never: 'Nie', rec_after_count: 'Nach Anzahl',
     rec_on_date: 'Am Datum', rec_occurrences: 'Termine',
     copy_to_calendar: 'Kopieren nach…', event_copied: 'Termin kopiert',
+    edit_before_copy: 'Vor dem Kopieren bearbeiten',
     event_updated: 'Termin aktualisiert', event_created: 'Termin erstellt',
     confirm_delete_event: '"{title}" wirklich löschen?',
     confirm_delete_title: 'Termin löschen',
@@ -361,6 +362,7 @@ const translations = {
     rec_ends: 'Ends', rec_never: 'Never', rec_after_count: 'After count',
     rec_on_date: 'On date', rec_occurrences: 'occurrences',
     copy_to_calendar: 'Copy to…', event_copied: 'Event copied',
+    edit_before_copy: 'Edit before copying',
     event_updated: 'Event updated', event_created: 'Event created',
     confirm_delete_event: 'Really delete "{title}"?',
     confirm_delete_title: 'Delete event',