fix: use ctx.getAllInterfaceFields in class-dispatch for inherited interface fields

[cs01]

Summary

• getInterfaceFromAST, and two field-search loops in class-dispatch.ts iterated interfaceDecl.fields directly, missing inherited fields from extends
• Added getAllInterfaceFields(iface: InterfaceDeclaration): InterfaceField[] to MethodCallGeneratorContext interface (delegates to existing LLVMGenerator.getAllInterfaceFields which already works correctly)
• All three sites now call ctx.getAllInterfaceFields() to include parent interface fields

Test plan

• All 428 unit tests pass
• Full 3-stage self-hosting passes (Stage 1 and Stage 2 both smoke-test clean)
• No regressions: object-keys, interface dispatch, and method routing tests pass

🤖 Generated with Claude Code