Refactor widgets & imports; add krow_domain

Add local krow_domain dependency to client, staff apps and client home package. Numerous UI/widget cleanups across features: add const where applicable, use explicit List<Widget> types and List<Widget>.generate, add super.key to constructors, tighten BlocProvider generics, replace some Containers with SizedBox, and simplify InputDecoration/Border constructors. Fix API error handler to return a const UnknownException. Update internal imports to package-style paths (staff_home, staff_payments, staff_main repository interface) and normalize Flutter imports (use material.dart). Add missing braces for early returns in tax form pages. Mostly formatting and small API/typing refactors with no behavioral changes intended.

apps/mobile/packages/features/client/billing/lib/src/presentation/widgets/invoices_list_skeleton.dart

@@ -26,10 +26,10 @@ class InvoicesListSkeleton extends StatelessWidget {
                 ),
                 child: Column(
                   crossAxisAlignment: CrossAxisAlignment.start,
-                  children: [
+                  children: <Widget>[
                     Row(
                       mainAxisAlignment: MainAxisAlignment.spaceBetween,
-                      children: [
+                      children: <Widget>[
                         UiShimmerBox(
                           width: 64,
                           height: 22,
@@ -47,10 +47,10 @@ class InvoicesListSkeleton extends StatelessWidget {
                     const SizedBox(height: UiConstants.space3),
                     Row(
                       mainAxisAlignment: MainAxisAlignment.spaceBetween,
-                      children: [
+                      children: <Widget>[
                         const Column(
                           crossAxisAlignment: CrossAxisAlignment.start,
-                          children: [
+                          children: <Widget>[
                             UiShimmerLine(width: 80, height: 10),
                             SizedBox(height: UiConstants.space1),
                             UiShimmerLine(width: 100, height: 20),