feat: Newsletter system improvements and validation framework

- Fix: Marketing events now display in Staff notifications tab
- Reorganize: Move Coupons to Marketing/Coupons for better organization
- Add: Comprehensive email/phone validation with extensible filter hooks
  - Email validation with regex pattern (xxxx@xxxx.xx)
  - Phone validation with WhatsApp verification support
  - Filter hooks for external API integration (QuickEmailVerification, etc.)
- Fix: Newsletter template routes now use centralized notification email builder
- Add: Validation.php class for reusable validation logic
- Add: VALIDATION_HOOKS.md documentation with integration examples
- Add: NEWSLETTER_CAMPAIGN_PLAN.md architecture for future campaign system
- Fix: API delete method call in Newsletter.tsx (delete -> del)
- Remove: Duplicate EmailTemplates.tsx (using notification system instead)
- Update: Newsletter controller to use centralized Validation class

Breaking changes:
- Coupons routes moved from /routes/Coupons to /routes/Marketing/Coupons
- Legacy /coupons routes maintained for backward compatibility

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

@@ -105,6 +105,7 @@ export default function NotificationEvents() {
   const orderEvents = eventsData?.orders || [];
   const productEvents = eventsData?.products || [];
   const customerEvents = eventsData?.customers || [];
+  const marketingEvents = eventsData?.marketing || [];
 
   return (
     <div className="space-y-6">
@@ -340,6 +341,77 @@ export default function NotificationEvents() {
           </div>
         </SettingsCard>
       )}
+
+      {/* Marketing Events */}
+      {marketingEvents.length > 0 && (
+        <SettingsCard
+          title={__('Marketing Events')}
+          description={__('Notifications about newsletter and marketing activities')}
+        >
+          <div className="space-y-6">
+            {marketingEvents.map((event: NotificationEvent) => (
+              <div key={event.id} className="pb-6 border-b last:border-0">
+                <div className="mb-4">
+                  <h3 className="font-medium text-sm">{event.label}</h3>
+                  <p className="text-xs text-muted-foreground mt-1">{event.description}</p>
+                </div>
+
+                <div className="space-y-3">
+                  {channels?.map((channel: NotificationChannel) => {
+                    const channelEnabled = event.channels?.[channel.id]?.enabled || false;
+                    const recipient = event.channels?.[channel.id]?.recipient || 'admin';
+
+                    return (
+                      <div
+                        key={channel.id}
+                        className="flex items-center justify-between p-3 rounded-lg border bg-card"
+                      >
+                        <div className="flex items-center gap-3">
+                          <div className={`p-2 rounded-lg ${channelEnabled ? 'bg-green-500/20 text-green-600' : 'bg-muted text-muted-foreground'}`}>
+                            {getChannelIcon(channel.id)}
+                          </div>
+                          <div>
+                            <div className="flex items-center gap-2">
+                              <span className="text-sm font-medium">{channel.label}</span>
+                              {channel.builtin && (
+                                <Badge variant="secondary" className="text-xs">
+                                  {__('Built-in')}
+                                </Badge>
+                              )}
+                            </div>
+                            {channelEnabled && (
+                              <span className="text-xs text-muted-foreground">
+                                {__('Send to')}: {recipient === 'admin' ? __('Admin') : recipient === 'customer' ? __('Customer') : __('Both')}
+                              </span>
+                            )}
+                          </div>
+                        </div>
+                        <div className="flex items-center gap-2">
+                          {channelEnabled && channel.enabled && (
+                            <Button
+                              variant="ghost"
+                              size="sm"
+                              onClick={() => openTemplateEditor(event.id, channel.id)}
+                              className="h-8 w-8 p-0"
+                            >
+                              <Settings className="h-4 w-4" />
+                            </Button>
+                          )}
+                          <Switch
+                            checked={channelEnabled}
+                            onCheckedChange={() => toggleChannel(event.id, channel.id, channelEnabled)}
+                            disabled={!channel.enabled || updateMutation.isPending}
+                          />
+                        </div>
+                      </div>
+                    );
+                  })}
+                </div>
+              </div>
+            ))}
+          </div>
+        </SettingsCard>
+      )}
     </div>
   );
 }