Add default hourly rate to client model

The changes add a new defaultHourlyRate field to clients, including form
updates and automatic rate propagation to invoices. Add default hourly
rate for clients

The subject line you provided already clearly expresses the changes, and
no additional context is needed in the body, so I'll keep just the
subject line.

src/components/forms/invoice-form.tsx

@@ -281,6 +281,20 @@ export function InvoiceForm({ invoiceId }: InvoiceFormProps) {
     }
   }, [businesses, formData.businessId, invoiceId]);
 
+  // Update default hourly rate when client changes
+  React.useEffect(() => {
+    if (formData.clientId && clients) {
+      const selectedClient = clients.find((c) => c.id === formData.clientId);
+      if (selectedClient?.defaultHourlyRate) {
+        setFormData((prev) => ({
+          ...prev,
+          defaultHourlyRate: selectedClient.defaultHourlyRate,
+        }));
+      }
+    }
+     
+  }, [formData.clientId, clients]);
+
   // Calculate totals
   const totals = React.useMemo(() => {
     const subtotal = formData.items.reduce(
@@ -339,7 +353,11 @@ export function InvoiceForm({ invoiceId }: InvoiceFormProps) {
     if (idx === 0) return; // Already at top
     setFormData((prev) => {
       const newItems = [...prev.items];
-      [newItems[idx - 1], newItems[idx]] = [newItems[idx], newItems[idx - 1]];
+      if (idx > 0 && idx < newItems.length) {
+        const temp = newItems[idx - 1]!;
+        newItems[idx - 1] = newItems[idx]!;
+        newItems[idx] = temp;
+      }
       return { ...prev, items: newItems };
     });
   };
@@ -349,7 +367,11 @@ export function InvoiceForm({ invoiceId }: InvoiceFormProps) {
     if (idx === formData.items.length - 1) return; // Already at bottom
     setFormData((prev) => {
       const newItems = [...prev.items];
-      [newItems[idx], newItems[idx + 1]] = [newItems[idx + 1], newItems[idx]];
+      if (idx >= 0 && idx < newItems.length - 1) {
+        const temp = newItems[idx]!;
+        newItems[idx] = newItems[idx + 1]!;
+        newItems[idx + 1] = temp;
+      }
       return { ...prev, items: newItems };
     });
   };