chore(ui): Refactor RelatedModels.tsx

Major cleanup of RelatedModels.tsx for improved readability, structure, and maintainability.
Dried out repetitive logic
Consolidated model type sorting into reusable helpers
Added disallowed model type relationships to prevent broken connections (e.g. VAE ↔ LoRA)
- Aware this introduces a new constraint—open to feedback (see PR comment)
Some naming and types may still need refinement; happy to revisit

Author: xiaden