Fix dashboard branch scoping: invoices don't have branch_id column

Invoices use billable morph (not direct branch_id). Scope through
whereHasMorph on the participant's branch_id instead.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Livewire/Dashboard.php

@@ -48,7 +48,7 @@ public function render()
                 ->when($branchId, fn ($q) => $q->where('branch_id', $branchId))->sum('amount'),
             'outstanding_invoices' => Invoice::whereIn('status', [
                 InvoiceStatus::Sent, InvoiceStatus::PartiallyPaid, InvoiceStatus::Overdue,
-            ])->when($branchId, fn ($q) => $q->where('branch_id', $branchId))->sum('due_amount'),
+            ])->when($branchId, fn ($q) => $q->whereHasMorph('billable', [Participant::class], fn ($p) => $p->where('branch_id', $branchId)))->sum('due_amount'),
             'pos_today' => POSTransaction::whereDate('processed_at', $today)
                 ->when($branchId, fn ($q) => $q->where('branch_id', $branchId))->sum('total_amount'),
             'pos_today_count' => POSTransaction::whereDate('processed_at', $today)
@@ -90,8 +90,8 @@ public function render()
             ->count();
 
         $overdueInvoices = Invoice::where('status', InvoiceStatus::Overdue)
-            ->when($branchId, fn ($q) => $q->where('branch_id', $branchId))
-            ->with('participant.person')
+            ->when($branchId, fn ($q) => $q->whereHasMorph('billable', [Participant::class], fn ($p) => $p->where('branch_id', $branchId)))
+            ->with('billable')
             ->orderBy('due_date')
             ->limit(5)
             ->get();