[enhancement] improve the elections simulator

[betich]

Tasks

• write custom date picker ui
• add github link to footer
• minor ui fixes

Write a custom calendar

The current calendar is from a random react library i found and it has some problems (notably when you choose the year in the picker, the year is displayed in ค.ศ. but it should be displayed in พ.ศ.). The library also opts in system-ui based theme picking, which is not intended.

The ui is quite janky, in some parts. These are some notable issues:

1. In the page (8), some mobile ui is janky for the "แตะเพื่อลงลายมือชื่อ" button

2. In some cases, the circle is not in the center of the image (4)
   

[betich]

pull requests are welcome btw