fix: resolve duplicate function errors and implement proper AST transformation infrastructure

- Replace broken index.ts with clean implementation (1231→410 lines)
- Remove hundreds of duplicate generic transform functions
- Implement proper 13→14 transformation with version-specific helpers
- Add enum imports and type casting for PG13/PG14 differences
- Fix A_Const transformation for structural changes between versions
- Add helper functions for arrays, optional nodes, and specific types
- Implement placeholder functions for 14→15, 15→16, 16→17 transformations
- Maintain sequential transformation chain (transformToLatest)

The transformation infrastructure is now ready for testing and further development.

Co-Authored-By: Dan Lynch <[email protected]>

Author: devin-ai-integration[bot]