Staff form HTTP 500 and icon fix

Fixes applied:
1. Removed PHP 7 dirname(__DIR__, 2) usage from admin/hrms/staff_form.php for PHP 5.6 compatibility.
2. Replaced Boxicons-only back icon with Font Awesome/fallback icon.
3. Added local icon fallback CSS because uploaded Employee Profile_files.zip does not include ../webfonts files referenced by all.min.css.
4. Added Bootstrap-less accordion fallback JS for public staff pages.

After upload:
- Overwrite files.
- Run /admin/hrms/staff_profile_schema_repair.php
- Clear browser cache with Ctrl+F5.