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>
+    </>
+  )
+}

app/(app)/payments/payments-client.tsx

@@ -305,7 +305,7 @@ export function PaymentsClient({ payments: initialPayments, members, integration
               </div>
               {error && <p className="font-mono text-xs text-red-500">{error}</p>}
               <div className="flex gap-3 pt-2">
-                <button type="button" onClick={() => setShowLogCash(false)} className="flex-1 border border-border text-foreground font-sans text-sm py-2 rounded hover:border-primary/50 transition">Cancel</button>
+                <button type="button" disabled={loading} onClick={() => setShowLogCash(false)} className="flex-1 border border-border text-foreground font-sans text-sm py-2 rounded hover:border-primary/50 transition disabled:opacity-60">Cancel</button>
                 <button type="submit" disabled={loading} className="flex-1 bg-primary text-white font-sans text-sm py-2 rounded hover:bg-primary/90 transition disabled:opacity-60">
                   {loading ? 'Logging...' : 'Log Payment'}
                 </button>