perf: true drop-in replacement - increase upload parallelism

Commit notes

Backend (already committed): - Rate limit: 100 → 1000 chunks/min (10x) - Concurrent uploads: 10 → 50 (5x) - Adaptive chunk sizing: 512KB-5MB based on file size - Batch initiate: 50 → 100 files per request

Frontend (this commit): - Chunk upload concurrency: 4 → 8 (2x) - File upload concurrency: 6 → 8 (1.3x) - Reverted to original components (no UI changes needed)

Total estimated improvement: 3-5x faster uploads No frontend component changes required - true drop-in replacement

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