Wire up wallet balance and gift cards at checkout; fix Square gift card option; fix account/rewards.php CSS; fix real PDO/schema bugs found along the way

Feature: checkout.php now lets logged-in customers apply existing wallet
balance or redeem a gift card code (which tops up wallet first, then
applies) toward their order total. Deduction is deferred to payment
success (markSquarePaymentResult in includes/square.php), never at order
creation, so an abandoned checkout never loses real wallet money - mirrors
how loyalty points already work here, unlike stock which is decremented
eagerly. payment.php gains a second Square Gift Card tab (payments.giftCard()
SDK method) alongside the card form, both hitting the same
create-square-payment.php endpoint since Square treats both source types
identically.

New api/apply-wallet-credit.php validates/quotes an amount without writing
anything - actual spend happens only via markSquarePaymentResult(). The
gift-card-to-wallet transaction logic was extracted out of
api/redeem-gift-card.php into a shared loyalty()->redeemGiftCardToWallet()
so the Wallet page and checkout both call the same code.

Also fixed three unrelated pre-existing bugs surfaced while testing this:
- loyalty.php awardPoints() reused the same named PDO parameter (:points)
  twice in one UPDATE - fails under real prepared statements, meaning
  loyalty points (and the email sent right after them) were silently never
  awarded for any order tied to a logged-in customer.
- redeemGiftCardToWallet (formerly inline in redeem-gift-card.php) referenced
  a gift_cards.updated_at column that does not exist in the schema, and used
  invalid enum values (gift_card_transactions.type=redeem,
  wallet_transactions.type=gift_card) that do not match the actual enum
  definitions - gift card redemption has likely never worked at all.
- account/rewards.php was missing the  line that loads
  account.css, unlike every other account/*.php page, so its sidebar/layout
  rendered unstyled.

api/apply-wallet-credit.php

@@ -0,0 +1,58 @@
+<?php
+/**
+ * Tom's Java Jive - Apply Wallet Credit / Gift Card at Checkout
+ *
+ * Validates and quotes an amount to apply toward the current order total.
+ * Does NOT deduct wallet balance here - that only happens once the Square
+ * payment actually succeeds (see markSquarePaymentResult() in
+ * includes/square.php), so an abandoned checkout never loses a customer's
+ * real wallet money. A gift card code, if given, is redeemed into wallet
+ * balance immediately (same as the Wallet page does) since that step is
+ * safe/reversible-in-spirit - only the *spending* of wallet balance at
+ * checkout is deferred to payment success.
+ */
+
+require_once __DIR__ . '/../includes/functions.php';
+require_once __DIR__ . '/../includes/auth.php';
+require_once __DIR__ . '/../includes/loyalty.php';
+
+header('Content-Type: application/json');
+
+if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
+    jsonResponse(['error' => 'Method not allowed'], 405);
+}
+
+if (!CustomerAuth::isLoggedIn()) {
+    jsonResponse(['error' => 'Please log in to use wallet balance or a gift card'], 401);
+}
+
+$customer = CustomerAuth::getFullUser();
+$input = json_decode(file_get_contents('php://input'), true);
+
+$orderTotal = (float) ($input['order_total'] ?? 0);
+if ($orderTotal <= 0) {
+    jsonResponse(['error' => 'Invalid order total'], 400);
+}
+
+$giftCardCode = trim($input['gift_card_code'] ?? '');
+
+if (!empty($giftCardCode)) {
+    $redeemResult = loyalty()->redeemGiftCardToWallet($customer['customer_id'], $giftCardCode);
+    if (!$redeemResult['success']) {
+        jsonResponse(['error' => $redeemResult['error']], 400);
+    }
+    $walletBalance = $redeemResult['new_balance'];
+} else {
+    $fresh = db()->fetch("SELECT wallet_balance FROM customers WHERE customer_id = :id", ['id' => $customer['customer_id']]);
+    $walletBalance = (float) ($fresh['wallet_balance'] ?? 0);
+}
+
+$requested   = isset($input['amount']) ? (float) $input['amount'] : $walletBalance;
+$applyAmount = max(0, round(min($requested, $walletBalance, $orderTotal), 2));
+
+jsonResponse([
+    'success'       => true,
+    'apply_amount'  => $applyAmount,
+    'wallet_balance' => $walletBalance,
+    'new_total'     => round($orderTotal - $applyAmount, 2)
+]);