fix(worksheets): Set showBorrowNotation to false for smart mode

Smart mode doesn't have the showBorrowNotation field in config, so
enrichedProblems had undefined for this field. This caused Typst
compilation errors.

Fix: Explicitly set showBorrowNotation to false for smart mode problems.

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

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

apps/web/src/app/create/worksheets/addition/typstGenerator.ts

@@ -84,6 +84,7 @@ function generatePageTypst(
       return {
         ...p,
         ...displayOptions,
+        showBorrowNotation: false, // Smart mode doesn't have borrow notation (yet)
       }
     } else {
       // Manual mode: Uniform display across all problems