chore: remove unused TUS and V2 upload components

Commit notes

Removed experimental files that aren't being used: - backend/src/routes/tus.ts - frontend/src/lib/upload/ (entire directory) - frontend/src/routes/library/components/*V2.svelte - frontend/src/routes/library/components/UploadResumePrompt.svelte

The performance improvements are now purely in: - backend: rate limits, adaptive chunk sizing - frontend/src/lib/api/upload.ts: increased parallelism

Co-authored-by: armin.naimi <[email redacted]>