just two comments: calendar entries are shown atm from date start to including date end. So when i enter an entry from some date 0:00 to the next date 0:00 (one day) it is shown as if it extends to days. 
The first day of week should be displayed according to current locale. It is not sunday everywhere. 

 Where is Sunday not the first day of the week? 🤔

#asknostr 

 e.g. Monday is - also according to ISO 8601 - the first day of week in the follwing countries🇩🇪 🇫🇷 🇬🇧 🇷🇺 🇪🇸 🇮🇹 🇵🇹 🇬🇷 🇸🇪 🇳🇴 🇩🇰 🇫🇮 🇳🇱 🇧🇪 🇦🇹 🇨🇭 🇮🇪 🇵🇱 🇨🇿 🇭🇺 🇸🇰 🇸🇮 🇭🇷 🇷🇸 🇧🇦 🇲🇪 🇧🇬 🇷🇴 🇹🇷 🇸🇾 🇯🇴 🇱🇧 🇮🇶 🇮🇷 🇸🇦 🇦🇪 🇶🇦 🇰🇼 🇧🇭 🇴🇲 🇾🇪 🇵🇰 🇮🇳 to name a few. 
best practice is to consider the current locale.