feat: add soft delete for classes with cascade to sessions and linked records

components/dashboard/dashboardService.js

@@ -24,8 +24,8 @@ const getAdminStats = async () => {
     Professor.countDocuments({}),
     Professor.countDocuments({ isActive: true }),
     Course.countDocuments({}),
-    Session.countDocuments({}),
-    Session.find({})
+    Session.countDocuments({ isDeleted: { $ne: true } }),
+    Session.find({ isDeleted: { $ne: true } })
       .sort({ day: -1 })
       .limit(8)
       .populate('course', 'title type')
@@ -75,7 +75,7 @@ const getAdminStats = async () => {
 
   // Daily sessions trend (same window)
   const dailySessionsRaw = await Session.aggregate([
-    { $match: { createdAt: { $gte: rangeStart } } },
+    { $match: { isDeleted: { $ne: true }, createdAt: { $gte: rangeStart } } },
     {
       $group: {
         _id: {