feat: add ShiftAssignmentCard widget and StaffShifts module

- Implemented ShiftAssignmentCard widget for displaying shift assignments with client details, pay calculation, and confirmation actions.
- Created StaffShiftsModule to manage dependencies, routes, and use cases related to staff shifts.
- Added necessary dependencies in pubspec.yaml and generated pubspec.lock.

apps/mobile/pubspec.lock

@@ -1100,6 +1100,13 @@ packages:
       relative: true
     source: path
     version: "0.0.1"
+  staff_shifts:
+    dependency: transitive
+    description:
+      path: "packages/features/staff/shifts"
+      relative: true
+    source: path
+    version: "0.0.1"
   staff_tax_forms:
     dependency: transitive
     description: