Add uv environment for tutorial notebooks

[jameskermode]

Summary

• add a repository-wide pyproject.toml and uv.lock covering dependencies used across the tutorials
• keep notebook install cells available for Colab while skipping them in managed local environments
• update notebook code for current MACE, ASE, Janus, and radial embedding APIs
• add portable XTB/tblite handling and the missing T04 fine-tuning support modules

Validation

• uv lock --check
• uv pip check (187 installed packages compatible)
• notebook schema validation for all 24 discovered notebook files
• controlled execution of all 10 canonical tutorial notebooks

Training, long molecular dynamics, downloads, geometry optimization, NEB, and destructive cells were skipped during controlled execution.

[jameskermode]

Full end-to-end validation completed for T01_MACE_Practice_I.ipynb on Apple Silicon using the uv-managed environment. All 27 code cells executed successfully in 488.3 seconds, including MACE training/evaluation, XTB comparison, both 2,000-step MACE MD runs, RDF analysis, and visualization cells.

The initial unrestricted run exposed a PyTorch/OpenMP deadlock. Commit da5514c adds the validated Apple Silicon thread guard; the complete rerun then passed with no error outputs.