feat(notebooks): add shared environment-bootstrap module and drift-check tooling

[petercorke]

Summary

• Adds docs/notebooks/_mvtb_nb_bootstrap.py, a single source of truth for installing the toolbox across local Jupyter, Google Colab, and JupyterLite/Pyodide, replacing the pattern of 13+ notebooks each hand-pasting their own slightly-drifted Colab-install snippet.
• Adds sync_bootstrap.py (regenerates each notebook's marked bootstrap cell from the template) and clear_outputs.py (pure-stdlib output clearing) — both support --check for CI and explicit file args for the commit hook.
• Adds .githooks/pre-commit, a plain git hook (not the pre-commit framework — see docs/notebooks/README.md for why) that applies both fixes silently at commit time and re-stages the result.
• Adds a docs.yml CI step running both scripts in --check mode as the backstop for machines without the hook installed.
• Adds tests/test_notebook_bootstrap.py covering the generator/clearer logic directly (marker detection, fix vs. check mode, idempotency).

This was prompted by machinevision-toolbox-python 2.2.0 shipping a broken JupyterLite "Try it Now" demo — tqdm was added as a real dependency but never added to the one notebook's hand-maintained micropip install list, and nothing tested it before release.

Not included, deliberately: no notebooks are migrated to use the marker cell yet — that's a follow-up change, so this PR is reviewable as tooling-only.

Test plan

• pytest tests/test_notebook_bootstrap.py — 10/10 pass
• ruff check clean on all new files
• Ran sync_bootstrap.py --check / clear_outputs.py --check against the real docs/notebooks/ — correctly report nothing to do (no notebooks migrated yet)
• Ran .githooks/pre-commit directly against a real staged commit — confirmed it doesn't touch the 16 existing notebooks it shouldn't
• Confirmed the generated bootstrap cell compiles under ast.PyCF_ALLOW_TOP_LEVEL_AWAIT (matches how a real Jupyter/IPython kernel executes top-level await in a cell)

🤖 Generated with Claude Code

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 critical · 17 high · 1 medium · 1 minor

Alerts:
⚠ 20 issues (≤ 0 issues of at least minor severity)

Results:
20 new issues

Category	Results
Security	1 minor 17 high 1 critical 1 medium

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🟢 Metrics 57 complexity · 4 duplication

Metric	Results
Complexity	57
Duplication	4

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