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.

constants/permissions.js

@@ -90,7 +90,16 @@ const PERMISSIONS = {
 
   // Pending student registrations
   PENDING_STUDENTS_READ: 'pending_students:read',
-  PENDING_STUDENTS_UPDATE: 'pending_students:update'
+  PENDING_STUDENTS_UPDATE: 'pending_students:update',
+
+  // Institutional expenses (used for financial reporting)
+  EXPENSES_CREATE: 'expenses:create',
+  EXPENSES_READ: 'expenses:read',
+  EXPENSES_UPDATE: 'expenses:update',
+  EXPENSES_DELETE: 'expenses:delete',
+
+  // Financial reports (professor share, class profitability, date-range analytics)
+  FINANCIAL_REPORTS_READ: 'financial_reports:read'
 };
 
 const ALL_PERMISSIONS = Object.values(PERMISSIONS);