feat: Restructure notifications - Staff and Customer separation (WIP)

## 🎯 Phase 1: Backend + Frontend Structure

### Backend Changes

**NotificationsController.php:**
- ✅ Added `/notifications/staff/events` endpoint
- ✅ Added `/notifications/customer/events` endpoint
- ✅ Created `get_all_events()` helper method
- ✅ Added `recipient_type` field to all events
- ✅ Filter events by recipient (staff vs customer)

### Frontend Changes

**Main Notifications Page:**
- ✅ Restructured to show cards for Staff, Customer, Activity Log
- ✅ Entry point with clear separation
- ✅ Modern card-based UI

**Staff Notifications:**
- ✅ Created `/settings/notifications/staff` route
- ✅ Moved Channels.tsx → Staff/Channels.tsx
- ✅ Moved Events.tsx → Staff/Events.tsx
- ✅ Updated Staff/Events to use `/notifications/staff/events`
- ✅ Fixed import paths

### Structure

```
Settings → Notifications
├── Staff Notifications (admin alerts)
│   ├── Channels (Email, Push)
│   ├── Events (Orders, Products, Customers)
│   └── Templates
└── Customer Notifications (customer emails)
    ├── Channels (Email, Push, SMS)
    ├── Events (Orders, Shipping, Account)
    └── Templates
```

---

**Next:** Customer notifications page + routes

admin-spa/src/routes/Settings/Notifications/Staff.tsx

@@ -0,0 +1,49 @@
+import React, { useState } from 'react';
+import { Link } from 'react-router-dom';
+import { SettingsLayout } from '../components/SettingsLayout';
+import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs';
+import { Button } from '@/components/ui/button';
+import { __ } from '@/lib/i18n';
+import { ChevronLeft } from 'lucide-react';
+import StaffChannels from './Staff/Channels';
+import StaffEvents from './Staff/Events';
+import NotificationTemplates from './Templates';
+
+export default function StaffNotifications() {
+  const [activeTab, setActiveTab] = useState('channels');
+
+  return (
+    <SettingsLayout
+      title={__('Staff Notifications')}
+      description={__('Configure notifications for admins and staff members')}
+      action={
+        <Link to="/settings/notifications">
+          <Button variant="ghost" size="sm">
+            <ChevronLeft className="mr-2 h-4 w-4" />
+            {__('Back to Notifications')}
+          </Button>
+        </Link>
+      }
+    >
+      <Tabs value={activeTab} onValueChange={setActiveTab} className="space-y-6">
+        <TabsList className="grid w-full grid-cols-3">
+          <TabsTrigger value="channels">{__('Channels')}</TabsTrigger>
+          <TabsTrigger value="events">{__('Events')}</TabsTrigger>
+          <TabsTrigger value="templates">{__('Templates')}</TabsTrigger>
+        </TabsList>
+
+        <TabsContent value="channels" className="space-y-4">
+          <StaffChannels />
+        </TabsContent>
+
+        <TabsContent value="events" className="space-y-4">
+          <StaffEvents />
+        </TabsContent>
+
+        <TabsContent value="templates" className="space-y-4">
+          <NotificationTemplates recipientType="staff" />
+        </TabsContent>
+      </Tabs>
+    </SettingsLayout>
+  );
+}