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)/dashboard/loading.tsx

@@ -0,0 +1,33 @@
+import { Skeleton } from '@/components/ui/skeleton'
+
+export default function DashboardLoading() {
+  return (
+    <div className="min-h-screen bg-background">
+      <div className="bg-sidebar px-4 md:px-6 py-3">
+        <Skeleton className="h-6 w-32" />
+      </div>
+      <div className="p-4 md:p-6 space-y-6">
+        <div className="grid grid-cols-2 lg:grid-cols-4 gap-3 md:gap-4">
+          {Array.from({ length: 4 }).map((_, i) => (
+            <div key={i} className="bg-card rounded border border-border p-4 md:p-5 space-y-3">
+              <Skeleton className="h-3 w-24" />
+              <Skeleton className="h-8 w-16" />
+              <Skeleton className="h-3 w-20" />
+            </div>
+          ))}
+        </div>
+        <div className="grid lg:grid-cols-[1fr_280px] gap-6">
+          <div className="space-y-3">
+            <Skeleton className="h-4 w-40" />
+            <Skeleton className="h-40 w-full rounded border border-border" />
+            <Skeleton className="h-40 w-full rounded border border-border" />
+          </div>
+          <div className="space-y-3">
+            <Skeleton className="h-32 w-full rounded border border-border" />
+            <Skeleton className="h-24 w-full rounded border border-border" />
+          </div>
+        </div>
+      </div>
+    </div>
+  )
+}