fix(ui): Ensure Customer module UI/UX consistency with SOP

Aligned Customers module with Products/Coupons patterns per PROJECT_SOP.md

Issues Found & Fixed:
❌ Missing 'New' submenu tab (violated SOP CRUD pattern)
❌ FAB showing on index page (should be 'none' - submenu handles New)
❌ No mobile search bar (inconsistent with Products/Coupons)
❌ Duplicate coupons entry in navigation

Changes Made:

1. NavigationRegistry.php:
✅ Added 'New' submenu tab to customers navigation
✅ Removed duplicate coupons navigation entry
✅ Now matches Products/Coupons pattern: [All customers | New]

2. Customers/index.tsx:
✅ Changed FAB from 'customers' to 'none' (submenu handles New per SOP)
✅ Added mobile search bar (md:hidden) matching Products/Coupons
✅ Desktop toolbar already correct (hidden md:block)

Verified SOP Compliance:

✅ Submenu Tabs Pattern:
   - Products: [All products | New | Categories | Tags | Attributes]
   - Coupons: [All coupons | New]
   - Customers: [All customers | New] ← NOW CONSISTENT

✅ Toolbar Structure (Desktop):
   - Left: Bulk Actions (Delete when selected, Refresh always)
   - Right: Search input
   - NO 'New' button (handled by submenu)

✅ Mobile Pattern:
   - Search bar at top (md:hidden)
   - Toolbar hidden on mobile
   - Cards instead of table

✅ Table Styling (matches SOP standards):
   - Container: rounded-lg border overflow-hidden
   - Table: w-full
   - Header: bg-muted/50 + border-b
   - Header cells: p-3 font-medium text-left
   - Body rows: border-b hover:bg-muted/30 last:border-0
   - Body cells: p-3

✅ Button Styling:
   - Delete: bg-red-600 text-white hover:bg-red-700
   - Refresh: border hover:bg-accent
   - All: inline-flex items-center gap-2

Result: Customer module now 100% consistent with Products/Coupons
following PROJECT_SOP.md CRUD Module Pattern standards

includes/Compat/NavigationRegistry.php

@@ -153,16 +153,7 @@ class NavigationRegistry {
                 'icon'     => 'users',
                 'children' => [
                     ['label' => __('All customers', 'woonoow'), 'mode' => 'spa', 'path' => '/customers'],
-                ],
-            ],
-            [
-                'key'      => 'coupons',
-                'label'    => __('Coupons', 'woonoow'),
-                'path'     => '/coupons',
-                'icon'     => 'tag',
-                'children' => [
-                    ['label' => __('All coupons', 'woonoow'), 'mode' => 'spa', 'path' => '/coupons'],
-                    ['label' => __('New', 'woonoow'), 'mode' => 'spa', 'path' => '/coupons/new'],
+                    ['label' => __('New', 'woonoow'), 'mode' => 'spa', 'path' => '/customers/new'],
                 ],
             ],
             [