chore: notebook maintenance and folder cleanup

[JessUWE]

• Update the notebook_examples to use the 2026 notebook
• Remove the duplicate notebook folder within the docs/source folder

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.92%. Comparing base (c7e1d05) to head (724b98d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #336   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files           9        9           
  Lines        1273     1273           
=======================================
  Hits         1272     1272           
  Misses          1        1           

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