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.

utils/errors.json

@@ -94,6 +94,11 @@
     "en": "Class not found.",
     "fa": "کلاس یافت نشد."
   },
+  "EXPENSE_NOT_FOUND": {
+    "statusCode": 404,
+    "en": "Expense record not found.",
+    "fa": "هزینه یافت نشد."
+  },
   "DEFAULT_ROLE_NOT_FOUND": {
     "statusCode": 500,
     "en": "Default user role was not found. Please seed the database.",