Enables all-day event drag and drop

Implements comprehensive drag and drop for all-day events, allowing movement within the header and conversion to timed events when dragged into the calendar grid.

Optimizes column detection with a cached bounding box strategy, improving performance and accuracy. Refactors event conversion logic and renames related event bus events for clarity.

docs/drag-drop-header-bug-analysis.md

@@ -17,7 +17,7 @@ Når en day event dragges op til headeren (for at konvertere til all-day) og der
 
 ### Trin 3: Mouse enters Header ⚠️ PROBLEM STARTER HER
 - **DragDropManager** (linje 95-112): Lytter til `header:mouseover`
-- Emitter `drag:convert-to-allday` event
+- Emitter `drag:convert-to-allday_event` event
 - **AllDayManager** (linje 232-285): `handleConvertToAllDay()`:
   - Opretter all-day event i header
   - **FJERNER original timed event permanent** (linje 274: `originalElement.remove()`)
@@ -25,7 +25,7 @@ Når en day event dragges op til headeren (for at konvertere til all-day) og der
 
 ### Trin 4: Mouse leaves Header (tilbage til grid) ⚠️ PROBLEM FORTSÆTTER
 - **DragDropManager** (linje 128-136): Lytter til `header:mouseleave`
-- Emitter `drag:convert-from-allday` event
+- Emitter `drag:convert-to-time_event` event
 - **AllDayManager** (linje 290-311): `handleConvertFromAllDay()`:
   - Fjerner all-day event fra container
   - Viser drag clone igen

docs/drag-drop-header-complete-bug-analysis.md

@@ -24,7 +24,7 @@ sequenceDiagram
     Note over Mouse: Dragger over header
     loop Hver mouseover event
         Mouse->>Header: mouseover
-        Header->>AllDay: drag:convert-to-allday
+        Header->>AllDay: drag:convert-to-allday_event
         AllDay->>AllDay: Opretter NYT all-day event ❌
         Note over AllDay: Ingen check for eksisterende!
     end