feat: Merge Templates tab into Events tab with toggle + gear icon pattern

✅ UI Restructuring:
- Removed Templates tab from Staff and Customer pages
- Merged template editing into Events tab
- Changed from 3 tabs to 2 tabs (Channels | Events)

✅ Toggle + Gear Icon Pattern (like Payment Methods):
- Toggle switch to enable/disable channel for each event
- Gear icon (⚙️) appears when channel is enabled
- Click gear to edit template for that event/channel combination

✅ Navigation Updates:
- Back button from Edit Template now navigates to Events tab
- Gear icon navigates with correct recipient type (staff/customer)

✅ Applied to Both:
- Staff Notifications → Events tab
- Customer Notifications → Events tab

✅ Benefits:
- Cleaner UI with fewer tabs
- More intuitive workflow (enable → configure)
- Consistent pattern across the app
- Less navigation depth

🎯 Next: Restructure Channel Configuration as separate section

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

@@ -423,7 +423,7 @@ export default function EditTemplate() {
               // Determine if staff or customer based on event category
               const isStaffEvent = template.event_category === 'staff' || eventId?.includes('admin') || eventId?.includes('staff');
               const page = isStaffEvent ? 'staff' : 'customer';
-              navigate(`/settings/notifications/${page}?tab=templates`);
+              navigate(`/settings/notifications/${page}?tab=events`);
             }}
             className="gap-2"
             title={__('Back')}