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.

docs/EventSystem-Analysis.md

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+# Calendar Event System Analysis
+
+## Overview
+Analysis of all events used in the Calendar Plantempus system, categorized by type and usage.
+
+## Core Events (25 events)
+*Defined in `src/constants/CoreEvents.ts`*
+
+### Lifecycle Events (3)
+- `core:initialized` - Calendar initialization complete
+- `core:ready` - Calendar ready for use
+- `core:destroyed` - Calendar cleanup complete
+
+### View Events (3)
+- `view:changed` - Calendar view changed (day/week/month)
+- `view:rendered` - View rendering complete
+- `workweek:changed` - Work week configuration changed
+
+### Navigation Events (4)
+- `nav:date-changed` - Current date changed
+- `nav:navigation-completed` - Navigation animation/transition complete
+- `nav:period-info-update` - Week/period information updated
+- `nav:navigate-to-event` - Request to navigate to specific event
+
+### Data Events (4)
+- `data:loading` - Data fetch started
+- `data:loaded` - Data fetch completed
+- `data:error` - Data fetch error
+- `data:events-filtered` - Events filtered
+
+### Grid Events (3)
+- `grid:rendered` - Grid rendering complete
+- `grid:clicked` - Grid cell clicked
+- `grid:cell-selected` - Grid cell selected
+
+### Event Management (4)
+- `event:created` - New event created
+- `event:updated` - Event updated
+- `event:deleted` - Event deleted
+- `event:selected` - Event selected
+
+### System Events (2)
+- `system:error` - System error occurred
+- `system:refresh` - Refresh requested
+
+### Filter Events (1)
+- `filter:changed` - Event filter changed
+
+### Rendering Events (1)
+- `events:rendered` - Events rendering complete
+
+## Custom Events (22 events)
+*Used throughout the system for specific functionality*
+
+### Drag & Drop Events (12)
+- `drag:start` - Drag operation started
+- `drag:move` - Drag operation in progress
+- `drag:end` - Drag operation ended
+- `drag:auto-scroll` - Auto-scroll during drag
+- `drag:column-change` - Dragged to different column
+- `drag:mouseenter-header` - Mouse entered header during drag
+- `drag:mouseleave-header` - Mouse left header during drag
+- `drag:convert-to-time_event` - Convert all-day to timed event
+
+### Event Interaction (2)
+- `event:click` - Event clicked (no drag)
+- `event:clicked` - Event clicked (legacy)
+
+### Header Events (3)
+- `header:mouseleave` - Mouse left header area
+- `header:height-changed` - Header height changed
+- `header:rebuilt` - Header DOM rebuilt
+
+### All-Day Events (1)
+- `allday:ensure-container` - Ensure all-day container exists
+
+### Column Events (1)
+- `column:mouseover` - Mouse over column
+
+### Scroll Events (1)
+- `scroll:to-event-time` - Scroll to specific event time
+
+### Workweek Events (1)
+- `workweek:header-update` - Update header after workweek change
+
+### Navigation Events (1)
+- `navigation:completed` - Navigation completed (different from core event)
+
+## Event Payload Analysis
+
+### Type Safety Issues Found
+
+#### 1. AllDayManager Event Mismatch
+**File:** `src/managers/AllDayManager.ts:33-34`
+```typescript
+// Expected payload:
+const { targetDate, originalElement } = (event as CustomEvent).detail;
+
+// Actual payload from DragDropManager:
+{
+  targetDate: string,
+  mousePosition: { x: number, y: number },
+  originalElement: HTMLElement,
+  cloneElement: HTMLElement | null
+}
+```
+
+#### 2. Inconsistent Event Signatures
+Multiple events have different payload structures across different emitters/listeners.
+
+#### 3. No Type Safety
+All events use `(event as CustomEvent).detail` without proper TypeScript interfaces.
+
+## Event Usage Statistics
+
+### Most Used Events
+1. **Drag Events** - 12 different types, used heavily in drag-drop system
+2. **Core Navigation** - 4 types, used across all managers
+3. **Grid Events** - 3 types, fundamental to calendar rendering
+4. **Header Events** - 3 types, critical for all-day functionality
+
+### Critical Events (High Impact)
+- `drag:mouseenter-header` / `drag:mouseleave-header` - Core drag functionality
+- `nav:navigation-completed` - Synchronizes multiple managers
+- `grid:rendered` - Triggers event rendering
+- `events:rendered` - Triggers filtering system
+
+### Simple Events (Low Impact)
+- `header:height-changed` - Simple notification
+- `allday:ensure-container` - Simple request
+- `system:refresh` - Simple trigger
+
+## Recommendations
+
+### Priority 1: Fix Critical Issues
+1. Fix AllDayManager event signature mismatch
+2. Standardize drag event payloads
+3. Document current event contracts
+
+### Priority 2: Type Safety Implementation
+1. Create TypeScript interfaces for all event payloads
+2. Implement type-safe EventBus
+3. Migrate drag events first (highest complexity)
+
+### Priority 3: System Cleanup
+1. Consolidate duplicate events (`event:click` vs `event:clicked`)
+2. Standardize event naming conventions
+3. Remove unused events
+
+## Total Event Count
+- **Core Events:** 25
+- **Custom Events:** 22
+- **Total:** 47 unique event types
+
+## Files Analyzed
+- `src/constants/CoreEvents.ts`
+- `src/managers/*.ts` (8 files)
+- `src/renderers/*.ts` (4 files)
+- `src/core/CalendarConfig.ts`
+
+*Analysis completed: 2025-09-20*