### What problem does this PR solve?
- Unify top level pages structure
- Standardize locale language codes (BCP 47) and time zones (IANA tz)
> **Note:**
> Newly created user info brings non-standard default values `timezone:
"UTC+8\tAsia/Shanghai"` and `language: "English"`.
### Type of change
- [x] Refactoring
### What problem does this PR solve?
Feat: Add FileUploadDialog #3221
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
feat: Add next login page with shadcn/ui #3221
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
