- Set all_day flag properly when creating VEvent in series handler
- Improve all-day event detection using VALUE=DATE parameter
- Add RFC-5545 compliance for exclusive end dates (backend adds 1 day)
- Fix end date display in event modal (frontend subtracts 1 day for display)
- Fix recurring all-day event expansion to maintain proper end date pattern
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Co-Authored-By: Claude <noreply@anthropic.com>