consolidate duplicated types across codegen files

[cs01]

Summary

• Consolidated InterfaceDefInfo from 4 duplicate definitions into 1 shared export in class-dispatch.ts
• Removed duplicate LiftedFunction interface from function-generator.ts (now imports from arrow-functions.ts)
• Replaced local NewMeta, ObjectNode, ClassNode type mirrors with proper AST types from ast/types.ts
• Replaced ExprBase interfaces with inline as { type: string } casts across 3 files
• Net reduction of ~33 lines

Test plan

• TypeScript type check passes
• npm run verify:quick passes (tests + Stage 1 self-hosting)

🤖 Generated with Claude Code