fix: avoid build-time root-owned cache env dirs

fix: set writable cache env vars for training space

chore: update comment on torchao shim strategy

revert: back to stable cu121 torch — patch applied at runtime

fix: use PyTorch nightly — torchao needs register_constant not in stable 2.6

fix: switch to cu124 wheels for torch==2.6.0 (cu121 tops out at 2.5.1)

fix: upgrade torch to 2.6.0 — torchao requires torch.int1 added in 2.6

fix: install unsloth_zoo before unsloth

fix: install unsloth in Dockerfile at build time (not at click-time)

fix: use python:3.11-slim base, install unsloth at runtime

feat: training space with manual start UI