Fixes drag and drop to header issues

Addresses two key issues related to dragging events to the header: the premature removal of the original event element and the creation of duplicate all-day events.

The original event is no longer removed when dragging to the header; it is now only removed upon a successful drop.

Also, it prevents the creation of duplicate all-day events by checking for existing all-day events before creating new ones, using DOM queries to ensure accurate state.

docs/drag-drop-header-implementation-details.md

@@ -0,0 +1,143 @@
+# Implementeringsdetaljer: Check for Eksisterende All-Day Event
+
+## Hvor skal checket implementeres?
+
+**Fil**: `src/managers/AllDayManager.ts`
+**Metode**: `handleConvertToAllDay()`
+**Linje**: Lige efter linje 232 (start af metoden)
+
+## Præcis Implementation
+
+```typescript
+// AllDayManager.ts - handleConvertToAllDay metode (linje 232)
+private handleConvertToAllDay(targetDate: string, originalElement: HTMLElement): void {
+    // Extract event data from original element
+    const eventId = originalElement.dataset.eventId;
+    const title = originalElement.dataset.title || originalElement.textContent || 'Untitled';
+    const type = originalElement.dataset.type || 'work';
+    const startStr = originalElement.dataset.start;
+    const endStr = originalElement.dataset.end;
+
+    if (!eventId || !startStr || !endStr) {
+        console.error('Original element missing required data (eventId, start, end)');
+        return;
+    }
+
+    // ===== NY KODE STARTER HER (efter linje 243) =====
+    
+    // CHECK 1: Er dette faktisk clone elementet?
+    const isClone = eventId.startsWith('clone-');
+    const actualEventId = isClone ? eventId.replace('clone-', '') : eventId;
+    
+    // CHECK 2: Eksisterer all-day event allerede?
+    const container = this.getAllDayContainer();
+    if (container) {
+        const existingAllDay = container.querySelector(
+            `swp-allday-event[data-event-id="${actualEventId}"]`
+        );
+        
+        if (existingAllDay) {
+            console.log(`All-day event for ${actualEventId} already exists, skipping creation`);
+            return; // Exit early - don't create duplicate
+        }
+    }
+    
+    // ===== NY KODE SLUTTER HER =====
+    
+    // Fortsæt med normal oprettelse...
+    // Create CalendarEvent for all-day conversion - preserve original times
+    const originalStart = new Date(startStr);
+    // ... resten af koden
+}
+```
+
+## Hvorfor virker dette?
+
+1. **Check for clone ID**: Vi checker om det draggede element er clone (starter med "clone-")
+2. **Normalisér ID**: Vi får det faktiske event ID uden "clone-" prefix
+3. **Query DOM**: Vi søger i all-day container efter eksisterende element med samme ID
+4. **Early exit**: Hvis det findes, logger vi og returnerer uden at oprette duplicate
+
+## Alternative Implementeringer
+
+### Option A: Track med Set (Hurtigere)
+```typescript
+// AllDayManager class property
+private activeAllDayEvents = new Set<string>();
+
+private handleConvertToAllDay(targetDate: string, originalElement: HTMLElement): void {
+    const eventId = originalElement.dataset.eventId;
+    const actualEventId = eventId?.startsWith('clone-') 
+        ? eventId.replace('clone-', '') 
+        : eventId;
+    
+    // Check i memory først (hurtigere)
+    if (this.activeAllDayEvents.has(actualEventId)) {
+        return;
+    }
+    
+    // Marker som aktiv
+    this.activeAllDayEvents.add(actualEventId);
+    
+    // ... opret all-day event
+}
+
+private handleConvertFromAllDay(draggedEventId: string): void {
+    // Fjern fra tracking
+    this.activeAllDayEvents.delete(draggedEventId);
+    
+    // ... fjern all-day event
+}
+```
+
+### Option B: Data Attribute Flag
+```typescript
+private handleConvertToAllDay(targetDate: string, originalElement: HTMLElement): void {
+    // Check flag på original element
+    if (originalElement.dataset.hasAllDayVersion === 'true') {
+        return;
+    }
+    
+    // Sæt flag
+    originalElement.dataset.hasAllDayVersion = 'true';
+    
+    // ... opret all-day event
+}
+
+private handleConvertFromAllDay(draggedEventId: string): void {
+    // Find original og fjern flag
+    const original = document.querySelector(`[data-event-id="${draggedEventId}"]`);
+    if (original) {
+        delete original.dataset.hasAllDayVersion;
+    }
+    
+    // ... fjern all-day event
+}
+```
+
+## Anbefalet Løsning
+
+**DOM Query Check** (første løsning) er mest robust fordi:
+1. Den checker faktisk DOM state
+2. Ingen ekstra state at vedligeholde
+3. Fungerer selv hvis events kommer ud af sync
+
+## Test Verification
+
+For at teste om det virker:
+1. Åbn browser console
+2. Drag et event langsomt over header
+3. Se efter "already exists" log messages
+4. Verificer kun ÉT all-day event i DOM med: 
+   ```javascript
+   document.querySelectorAll('swp-allday-event').length
+   ```
+
+## Linje 274 Fix
+
+Samtidig skal vi fjerne/kommentere linje 274:
+```typescript
+// originalElement.remove();  // <-- KOMMENTER DENNE UD
+```
+
+Dette sikrer original element ikke fjernes for tidligt.