Simplify self-service payments to full-amount checkout, add manual-page payment tab

Self-service "pay now" flows (registration success + user dashboard) now go
straight to a Yoco checkout for the full outstanding balance instead of
prompting for a partial amount; that page has been removed. Partial-amount
payment links remain supervisor/admin-only via the Payments dashboard.

Also adds a "Record Payment" tab to the supervisor manual registration page,
pre-filled with the most recently created registration, so staff can capture
a payment right after registering someone without leaving the page.

frontend/src/app/registration/success/page.tsx

@@ -22,6 +22,7 @@ function RegistrationSuccessContent() {
   const [loading, setLoading] = React.useState(false);
   const [error, setError] = React.useState<string | null>(null);
   const [info, setInfo] = React.useState<string | null>(null);
+  const [payLoading, setPayLoading] = React.useState(false);
 
   React.useEffect(() => {
     (async () => {
@@ -79,9 +80,32 @@ function RegistrationSuccessContent() {
     }
   }, [reg, totalDue, router]);
 
-  const goPay = () => {
+  const goPay = async () => {
     if (!registrationId) return;
-    router.push(`/dashboard/user/pay?registrationId=${encodeURIComponent(registrationId)}`);
+    const token = (typeof window !== 'undefined') ? localStorage.getItem('token') : null;
+    if (!token) { setError('Please login to pay.'); return; }
+    try {
+      setError(null);
+      setPayLoading(true);
+      const { createFullPaymentCheckout } = await import('@/lib/api');
+      const res = await createFullPaymentCheckout(token, registrationId);
+      if (res.priceUpdated) {
+        // Early-bird price changed since registration — surface the new total and
+        // reload the registration so the displayed totalDue reflects it, instead of redirecting.
+        setError(`${res.message || 'Pricing has changed.'} New total: R ${(res.newTotal ?? 0).toFixed(2)}. Please try again.`);
+        try {
+          const r = await (await import('@/lib/api')).apiFetch(`/api/registrations/${encodeURIComponent(registrationId)}`, { authToken: token });
+          if (r) setReg(r);
+        } catch {}
+        return;
+      }
+      if (!res.redirectUrl) { setError('Failed to create checkout'); return; }
+      window.location.href = res.redirectUrl;
+    } catch (e: any) {
+      setError(e?.message || 'Failed to create checkout');
+    } finally {
+      setPayLoading(false);
+    }
   };
 
   const goDashboard = () => {
@@ -108,9 +132,9 @@ function RegistrationSuccessContent() {
             {(totalDue > 0 || (!reg && fallbackTotalDue > 0)) && (
               <button
                 onClick={goPay}
-                disabled={!registrationId}
+                disabled={!registrationId || payLoading}
                 className="px-4 py-2 rounded bg-green-600 text-white disabled:opacity-60"
-              >Pay with Yoco</button>
+              >{payLoading ? "Creating checkout..." : "Pay with Yoco"}</button>
             )}
             <button
               onClick={goDashboard}