Add professor share & financial reports UI, expense management page

Adds payout configuration fields (percentage/hourly + per-session
expense allowance) with a live payout preview to the class form,
a new Financial Reports page (per-class and date-range/monthly tabs,
per-session drill-down dialog) with reusable stat cards, and an
Institutional Expenses management page. Registers routes, sidebar
navigation, and permission constants for the new financial_reports
and expenses permissions.

src/utils/professorShare.test.js

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+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  calculateSessionDurationHours,
+  resolveSessionDurationHours,
+  calculatePercentageShare,
+  calculateHourlyShare,
+  calculateExtraExpenses,
+  calculateProfessorPayout,
+  calculateNetProfit,
+  calculatePendingReceivables,
+  calculateOverpaidAmount
+} from './professorShare.js';
+
+describe('calculateSessionDurationHours', () => {
+  it('computes duration between two clock times', () => {
+    assert.equal(calculateSessionDurationHours('18:00', '20:00'), 2);
+  });
+
+  it('returns 0 for invalid input', () => {
+    assert.equal(calculateSessionDurationHours('', ''), 0);
+    assert.equal(calculateSessionDurationHours(null, undefined), 0);
+  });
+});
+
+describe('resolveSessionDurationHours', () => {
+  it('prefers hoursPerSection over the class time window', () => {
+    assert.equal(resolveSessionDurationHours({ hoursPerSection: 2, startTime: '18:00', endTime: '20:30' }), 2);
+  });
+
+  it('falls back to the class time window', () => {
+    assert.equal(resolveSessionDurationHours({ startTime: '18:00', endTime: '19:30' }), 1.5);
+  });
+});
+
+describe('calculateProfessorPayout', () => {
+  it('computes percentage-based payout with extra expenses', () => {
+    const result = calculateProfessorPayout({
+      payoutType: 'percentage',
+      payoutPercentage: 40,
+      revenue: 10_000_000,
+      extraExpensePerSession: 100_000,
+      sessionsCount: 5
+    });
+    assert.equal(result.baseShare, 4_000_000);
+    assert.equal(result.extraExpenses, 500_000);
+    assert.equal(result.totalPayout, 4_500_000);
+  });
+
+  it('computes hourly-based payout with extra expenses', () => {
+    const result = calculateProfessorPayout({
+      payoutType: 'hourly',
+      payoutHourlyRate: 300_000,
+      sessionDurationHours: 1.5,
+      extraExpensePerSession: 80_000,
+      sessionsCount: 10
+    });
+    assert.equal(result.baseShare, 4_500_000);
+    assert.equal(result.extraExpenses, 800_000);
+    assert.equal(result.totalPayout, 5_300_000);
+  });
+});
+
+describe('calculateNetProfit', () => {
+  it('can go negative to represent a loss', () => {
+    assert.equal(calculateNetProfit({ totalIncome: 1_000_000, professorTotalPayout: 4_500_000 }), -3_500_000);
+  });
+});
+
+describe('calculatePendingReceivables / calculateOverpaidAmount', () => {
+  it('never returns negative outstanding, and surfaces overpayments separately', () => {
+    assert.equal(calculatePendingReceivables(10_000_000, 12_000_000), 0);
+    assert.equal(calculateOverpaidAmount(10_000_000, 12_000_000), 2_000_000);
+  });
+
+  it('handles zero revenue classes gracefully', () => {
+    assert.equal(calculatePendingReceivables(0, 0), 0);
+    assert.equal(calculateExtraExpenses({}), 0);
+  });
+});