feat: UI nav, onboarding, L2CS weights path + torch.load; trim dev files

Integrate L2CS-Net gaze estimation

MERGE EVERYTHING from feature/integration-cleaned :((((((((((((((((((((((((((((((((((((((((((((((( so tired

evaluation: channel ablation script + feature importance LOPO

chore: integration cleanup — remove eye CNN, add threshold justification, fix pipeline

Merge UI Manually (expect main)

Put all the models together (expect UI)