fix(worksheets): add backward compatibility for displayRules in SmartModeControls

Use type casting to safely access borrowNotation and borrowingHints fields
from formState.displayRules, which may not have these fields if coming from
old worksheet configurations.

Provides fallback to profile defaults when fields are missing.

🤖 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

@@ -77,7 +77,7 @@ function generatePageTypst(
           ? analyzeProblem(p.a, p.b)
           : analyzeSubtractionProblem(p.minuend, p.subtrahend);
       const displayOptions = resolveDisplayForProblem(
-        config.displayRules,
+        config.displayRules as any, // Cast for backward compatibility with configs missing new fields
         meta,
       );