Add Steane global rotation demo

[caijintaoduolacmeng-star]

Summary

• Add a docs demo notebook reproducing the Steane [[7,1,3]] global-rotation curve from Fig. 4a of the Nature FTQC paper.
• Include stabilizer/logical observable sampling, postselection, and an unentangled reference curve.
• Wire the notebook into the Tutorials navigation.

Verification

• Executed docs/demos/global_rotation_steane.ipynb with nbclient: 16 cells passed.
• mkdocs build --strict was attempted, but the existing encoding_demo.ipynb requires tesseract_decoder, which is unavailable for this local Windows/Python environment.

[caijintaoduolacmeng-star]

I checked the two failing checks. The code-related checks are green (build, ruff, black, pyright, isort). The remaining failures look permission-related for a fork PR rather than caused by this change:

• Deploy preview documentation fails when github-actions[bot] tries to push to QuEraComputing/tsim.git gh-pages and receives 403.
• post downloads coverage successfully, reports average coverage 97%, then fails with Resource not accessible by integration when the coverage action tries to post/update GitHub data.

I do not see a code change needed from this PR for those two checks.