fix: WordPress forms.css override and cache invalidation

🔴 Issue 1: WordPress forms.css Breaking Input Styling (FIXED)
Problem: /wp-admin/css/forms.css overriding our input styles
- box-shadow: 0 0 0 transparent
- border-radius: 4px
- background-color: #fff
- color: #2c3338

Solution:
- Added !important overrides to Input component
- !bg-transparent !border-input !rounded-md !shadow-sm
- Forces our shadcn styles over WordPress admin CSS

Result: ✅ Inputs now look consistent regardless of WP admin CSS

🔴 Issue 2: Toggle Not Saving + Toast Lying (FIXED)
Problem:
- Toggle appears to work but doesn't persist
- Response shows enabled: false but toast says 'enabled'
- WooCommerce gateway cache not clearing

Root Cause:
- WC()->payment_gateways()->payment_gateways() returns cached data
- wp_cache_delete not enough
- Need to force WooCommerce to reload gateways

Solution:
Backend (PaymentGatewaysProvider.php):
- wp_cache_flush() after save
- WC()->payment_gateways()->init() to reload
- Clear cache before fetching updated gateway

Frontend (Payments.tsx):
- await queryClient.invalidateQueries()
- Show toast AFTER refetch completes
- No more lying toast

Result: ✅ Toggle saves correctly + honest toast timing

📋 Technical Details:

WooCommerce Cache Layers:
1. wp_cache (object cache)
2. WC()->payment_gateways() internal cache
3. Gateway instance settings cache

Our Fix:
1. Save to DB
2. wp_cache_flush()
3. WC()->payment_gateways()->init()
4. Fetch fresh data
5. Return to frontend

Files Modified:
- input.tsx: !important overrides for WP admin CSS
- PaymentGatewaysProvider.php: Force WC reload
- PaymentsController.php: Clear cache before fetch
- Payments.tsx: Await invalidation before toast

🎯 Result:
✅ Inputs look perfect (no WP CSS interference)
✅ Toggle saves and persists correctly
✅ Toast shows after real state confirmed

includes/Api/PaymentsController.php

@@ -223,7 +223,10 @@ class PaymentsController extends WP_REST_Controller {
                 return $result;
             }
             
-            // Return updated gateway data
+            // Clear cache before fetching updated gateway
+            wp_cache_flush();
+            
+            // Return updated gateway data (fresh from DB)
             $gateway = PaymentGatewaysProvider::get_gateway($gateway_id);
             
             return rest_ensure_response([