fix: correct mathematical inconsistency in cascading complement test

Changed 99 + 8 test from '(100 - 90) + (10 - 2)' to '(100 - 90 - 2)'
to fix mathematical error where (100-90)+(10-2) = 18 ≠ 8.

The correct cascading complement shows: 100 - 90 - 2 = 8 ✓

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/utils/__tests__/pedagogicalAlgorithmTests.test.ts

@@ -288,7 +288,7 @@ describe('Pedagogical Expansion Algorithm - Addition Only', () => {
       {
         start: 99, target: 107,
         expected: {
-          decomposition: '99 + 8 = 99 + (100 - 90) + (10 - 2) = 107',
+          decomposition: '99 + 8 = 99 + (100 - 90 - 2) = 107',
           meaningful: true,
           steps: [
             { term: '100', value: 199, instruction: /add.*1.*hundreds/i },