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/classes/classModel.js

@@ -79,6 +79,31 @@ const classSchema = new mongoose.Schema({
     min: 1,
     default: null
   },
+  /** Professor compensation model for this class */
+  payoutType: {
+    type: String,
+    enum: ['percentage', 'hourly'],
+    default: 'percentage'
+  },
+  /** Used when payoutType === 'percentage' — professor's share of class revenue (0-100) */
+  payoutPercentage: {
+    type: Number,
+    default: 0,
+    min: 0,
+    max: 100
+  },
+  /** Used when payoutType === 'hourly' — professor's rate per teaching hour (Toman) */
+  payoutHourlyRate: {
+    type: Number,
+    default: 0,
+    min: 0
+  },
+  /** Optional flat allowance (travel/catering/etc.) paid per session held, regardless of payout model */
+  extraExpensePerSession: {
+    type: Number,
+    default: 0,
+    min: 0
+  },
   isActive: {
     type: Boolean,
     default: true