feat(ux): content-shaped route skeletons + disable Cancel during submit

Per-route loading.tsx for dashboard/members/payments (content-shaped
Skeletons instead of the single global full-page spinner) so heavy
server pages paint structure immediately. Add/Edit member + Log cash
modals now disable Cancel while the submit is in flight (was clickable
mid-insert).

app/(app)/payments/loading.tsx

@@ -0,0 +1,30 @@
+import { Skeleton } from '@/components/ui/skeleton'
+
+export default function PaymentsLoading() {
+  return (
+    <>
+      <div className="bg-sidebar px-4 md:px-6 py-3 flex items-center justify-between">
+        <Skeleton className="h-6 w-28" />
+        <div className="flex gap-2">
+          <Skeleton className="h-8 w-24" />
+          <Skeleton className="h-8 w-24" />
+        </div>
+      </div>
+      <div className="p-4 md:p-6 space-y-4">
+        <div className="grid grid-cols-2 lg:grid-cols-4 gap-3">
+          {Array.from({ length: 4 }).map((_, i) => <Skeleton key={i} className="h-20 w-full rounded border border-border" />)}
+        </div>
+        <div className="rounded-lg border border-border divide-y divide-border">
+          {Array.from({ length: 8 }).map((_, i) => (
+            <div key={i} className="px-4 py-3 flex items-center gap-4">
+              <Skeleton className="h-4 w-24" />
+              <Skeleton className="h-4 flex-1 max-w-[30%]" />
+              <Skeleton className="h-4 w-20" />
+              <Skeleton className="h-7 w-20" />
+            </div>
+          ))}
+        </div>
+      </div>
+    </>
+  )
+}