Improve join-us form & move to other location

[wen-templari]

### Tasks
- [ ] Add form validation
- [ ] Redesign form fields
- [ ] Add debounce for submit button
- [x] Add notification at UI after submit

[LazuliKao]

主要在：https://github.com/nbtca/Home/blob/main/src/pages/freshman/react/join.tsx
提交中 提交按钮转圈等等
关于重复提交的校验可能需要修改后端active

[LazuliKao]

后端增加提交时间字段
https://github.com/nbtca/active

[fananly233]

@LazuliKao finish

[LazuliKao]

备案问题，加入社团表单不可放在主页（个人网站）