feat: redesign calendar event modal for mobile

Compact, icon-driven layout inspired by Google Calendar:
- Icon-row layout with left-aligned icons for each field
- Color accent bar and save button match selected calendar color
- Toggle switch for all-day instead of checkbox
- Compact From/To time inputs
- Tighter spacing throughout, smaller font sizes
- German translations for all labels
- Footer bar with subtle background
- Shorter delete buttons for recurring events (This/Future/All)

v1.74.0

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "my-weekly-todo-list",
-  "version": "1.73.3",
+  "version": "1.74.0",
   "description": "A web-based weekly task management application that organizes to-dos and calendar events in a single, intuitive weekly view",
   "main": "index.js",
   "scripts": {