Add professor share calculation and financial reporting feature

Introduces per-class payout configuration (percentage or hourly rate,
plus an optional per-session expense allowance), pure calculation
utilities for professor payout/net profit/receivables, and a new
financial-reports API surface with per-class, per-session, and
date-range/monthly reports. Also adds full CRUD for institutional
expenses used in the range report, and wires up the new permissions
and roles. Fixes a pre-existing ReferenceError (missing
parseImportDate import) in paymentService that blocked creating
payments with dated transactions.

components/expenses/expenseModel.js

@@ -0,0 +1,43 @@
+// /components/expenses/expenseModel.js
+'use strict';
+
+const mongoose = require('mongoose');
+
+const expenseSchema = new mongoose.Schema({
+  title: {
+    type: String,
+    required: true,
+    trim: true
+  },
+  /** Free-form category label (e.g. "اجاره", "قبوض", "تجهیزات") */
+  category: {
+    type: String,
+    trim: true,
+    default: 'عمومی'
+  },
+  amount: {
+    type: Number,
+    required: true,
+    min: 0
+  },
+  /** Date the expense applies to — used to bucket expenses into date-range/monthly reports */
+  date: {
+    type: Date,
+    required: true
+  },
+  notes: {
+    type: String,
+    trim: true,
+    maxlength: 2000
+  },
+  recordedBy: {
+    type: mongoose.Schema.Types.ObjectId,
+    ref: 'User'
+  }
+}, {
+  timestamps: true
+});
+
+expenseSchema.index({ date: -1 });
+
+module.exports = mongoose.model('Expense', expenseSchema);