feat: Add event detail modal with markdown rendering and editing

This PR adds the ability to click on timeline events to view and edit their details:

## Features
- **Event Detail Modal**: Click any event in the timeline to open a modal showing:
  - Event title and date range (with time support)
  - Tags
  - Full markdown-rendered description

- **Edit Mode**: Two editing modes available:
  - Split View: Source editor + live preview side by side
  - Source Only: Simple textarea for quick edits

- **Expand Button**: Make the modal larger for more editing space

- **File Switching Fix**: Fixed an issue where switching between .mw files would cause colors to disappear and clicks to become unreliable

## Technical Changes
- New `EventDetailModal.ts` class for the modal UI
- Message handler in `MarkwhenView.ts` for `setDetailPath` events from timeline iframe
- `forceRefreshVisualization()` method to ensure proper state sync on file switch
- Comprehensive CSS styling for the modal and split view

Closes #4, Related to #22, #43

Author: cybersader