chore(codegen): fix convention violations from plan implementation review

- Add TODO(#360) for ResolveExpressionTypeFromSymbols codegen-layer
  workaround that should be moved to the semantic phase
- Use List<T>.Find() instead of LINQ FirstOrDefault() for consistency
  in IsEnumInstance() MemberAccess fallback

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: antonsynd

src/Sharpy.Compiler/CodeGen/RoslynEmitter.Expressions.cs

@@ -239,6 +239,7 @@ private ExpressionSyntax GenerateStringLiteral(StringLiteral literal)
     /// <summary>
     /// Fallback type resolution when SemanticInfo doesn't have an expression type recorded.
     /// Resolves identifiers via their symbol and member access (self.x) via the current type's fields/properties.
+    /// TODO(#360): This is a codegen-layer workaround — move type resolution to the semantic phase.
     /// </summary>
     private SemanticType? ResolveExpressionTypeFromSymbols(Sharpy.Compiler.Parser.Ast.Expression expr)
     {

src/Sharpy.Compiler/CodeGen/RoslynEmitter.Operators.cs

@@ -965,15 +965,15 @@ private bool IsEnumInstance(Expression expr)
             var objectType = GetExpressionSemanticType(memberAccess.Object);
             if (objectType is Semantic.UserDefinedType objUdt && objUdt.Symbol is TypeSymbol typeSymbol)
             {
-                var field = typeSymbol.Fields.FirstOrDefault(f => f.Name == memberAccess.Member);
+                var field = typeSymbol.Fields.Find(f => f.Name == memberAccess.Member);
                 if (field != null &&
                     GetVariableType(field) is Semantic.UserDefinedType fieldUdt &&
                     fieldUdt.Symbol?.TypeKind == Semantic.TypeKind.Enum)
                 {
                     return true;
                 }
 
-                var prop = typeSymbol.Properties.FirstOrDefault(p => p.Name == memberAccess.Member);
+                var prop = typeSymbol.Properties.Find(p => p.Name == memberAccess.Member);
                 if (prop?.Type is Semantic.UserDefinedType propUdt &&
                     propUdt.Symbol?.TypeKind == Semantic.TypeKind.Enum)
                 {