refactor: replace 5 inline type assertions with named ast types

[cs01]

Summary

• Replace 5 as { ... } inline type assertions with proper named AST types from ast/types.ts
• Prevents potential native compiler struct misalignment bugs (same class of bug as Set fix in fix: use SetNode type for Set<string> allocation, fixing native compiler codegen bug #222)
• Files: console.ts (UnaryNode), control-flow.ts (CallNode), variable-allocator.ts (VariableNode), llvm-generator.ts (EnumDeclaration), class.ts (ClassNode)

Test plan

• verify:quick passes including self-hosting Stage 1
• No behavioral change — all casts happened to have correct field ordering already