feat: add staff tax forms module with I-9 and W-4 forms

- Created staff_tax_forms_module.dart to manage tax forms feature.
- Implemented routes for TaxFormsPage, FormI9Page, and FormW4Page.
- Added mock repository for tax forms.
- Established necessary dependencies in pubspec.yaml.
- Exported module in staff_tax_forms.dart.

apps/mobile/packages/features/staff/staff_main/pubspec.yaml

@@ -35,6 +35,8 @@ dependencies:
     path: ../profile_sections/onboarding/experience
   staff_bank_account:
     path: ../profile_sections/finances/staff_bank_account
+  staff_tax_forms:
+    path: ../profile_sections/compliance/tax_forms
   # staff_shifts:
   #   path: ../shifts
   # staff_payments: