fix: replace inline anonymous type assertions with named ast types in…

[cs01]

Summary

• Replaced ~25 inline anonymous multi-field type assertions (as { type: string; name: string }) in src/codegen/ with named AST types from src/ast/types.ts
• Fixes latent SIGSEGV crashes in the native compiler: accessing index > 0 fields on anonymous inline types through union-typed interface fields (like Expression) triggers csyyjson_obj_get on flat pointer arrays instead of direct GEP
• Left integer-analysis.ts unchanged (5 hits) — those use object[] params, not union-typed interface fields, and are safe by design

Test plan

• npm test — all 426 tests pass
• bash scripts/self-hosting.sh --quick — Stage 0 and Stage 1 self-hosting succeed