Improves drag-drop event system with type safety

Introduces dedicated TypeScript interfaces for all drag-and-drop event payloads, enhancing type safety and developer experience.

Centralizes drag event detection and emission within `DragDropManager`. Refactors `AllDayManager`, `HeaderManager`, and `EventRendererManager` to subscribe to these typed events, improving decoupling and clarifying responsibilities.

Resolves known inconsistencies in drag event payloads, especially for all-day event conversions. Adds a comprehensive analysis document (`docs/EventSystem-Analysis.md`) detailing the event system and planned improvements.

src/types/EventTypes.ts

@@ -30,4 +30,59 @@ export interface TimeEvent {
   };
 }
 
-export type CalendarEventData = AllDayEvent | TimeEvent;
+export type CalendarEventData = AllDayEvent | TimeEvent;
+
+/**
+ * Drag Event Payload Interfaces
+ * Type-safe interfaces for drag and drop events
+ */
+
+// Common position interface
+export interface MousePosition {
+  x: number;
+  y: number;
+}
+
+// Drag start event payload
+export interface DragStartEventPayload {
+  draggedElement: HTMLElement;
+  mousePosition: MousePosition;
+  mouseOffset: MousePosition;
+  column: string | null;
+}
+
+// Drag move event payload
+export interface DragMoveEventPayload {
+  draggedElement: HTMLElement;
+  mousePosition: MousePosition;
+  mouseOffset: MousePosition;
+  snappedY: number;
+  column: string | null;
+}
+
+// Drag end event payload
+export interface DragEndEventPayload {
+  draggedElement: HTMLElement;
+  mousePosition: MousePosition;
+  finalPosition: {
+    column: string | null;
+    snappedY: number;
+  };
+  target: 'swp-day-column' | 'swp-day-header' | null;
+}
+
+// Drag mouse enter header event payload
+export interface DragMouseEnterHeaderEventPayload {
+  targetDate: string;
+  mousePosition: MousePosition;
+  originalElement: HTMLElement | null;
+  cloneElement: HTMLElement | null;
+}
+
+// Drag mouse leave header event payload
+export interface DragMouseLeaveHeaderEventPayload {
+  targetDate: string | null;
+  mousePosition: MousePosition;
+  originalElement: HTMLElement| null;
+  cloneElement: HTMLElement| null;
+}