perf: reduce retry limit from 3000 to 100 in problem generators

**Problem**: Large worksheets with constrained digit ranges were hanging.
Example: 1000 single-digit problems with 100% regrouping = 168,608 retries
for just 100 problems (1,686 retries/problem on average).

**Root Cause**: Only 9 single-digit numbers (1-9) with 100% regrouping
requirement = very few valid unique combinations. The 3000-retry limit
meant millions of iterations for 1000-2000 problem worksheets.

**Solution**: Reduced retry limit from 3000 to 100 in both:
- generateProblems() (addition)
- generateSubtractionProblems()

This allows some duplicate problems when the constraint space is tight,
but prevents the server from hanging on large worksheet generation.

**Impact**: 100-page worksheets should now generate in seconds instead
of timing out.

apps/web/src/app/create/worksheets/problemGenerator.ts

@@ -283,9 +283,11 @@ export function generateProblems(
     }
 
     // Generate problem with retries for uniqueness
+    // Reduced from 3000 to 100 - for large worksheets with constrained digit ranges,
+    // 3000 retries per problem = millions of iterations. Better to allow some duplicates.
     let tries = 0
     let ok = false
-    while (tries++ < 3000 && !ok) {
+    while (tries++ < 100 && !ok) {
       let a: number, b: number
       if (picked === 'both') {
         ;[a, b] = generateBoth(rand, minDigits, maxDigits)
@@ -613,9 +615,11 @@ export function generateSubtractionProblems(
     }
 
     // Generate problem with retries for uniqueness
+    // Reduced from 3000 to 100 - for large worksheets with constrained digit ranges,
+    // 3000 retries per problem = millions of iterations. Better to allow some duplicates.
     let tries = 0
     let ok = false
-    while (tries++ < 3000 && !ok) {
+    while (tries++ < 100 && !ok) {
       let minuend: number, subtrahend: number
       if (picked === 'both') {
         ;[minuend, subtrahend] = generateBothBorrow(rand, minDigits, maxDigits)