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/packages/features/staff/shifts/analysis_options.yaml

@@ -0,0 +1,5 @@
+include: package:flutter_lints/flutter.yaml
+
+linter:
+  rules:
+    # Add project specific rules here