remove bash preambles from cookbook notebooks

[Geochelone666]

remove the installation and clone setup cells from all five cookbook notebooks, including their saved output. the remaining cells are unchanged.

checked with [dev,all_extras,notebook_test] on python 3.12:

• all five notebooks load with nbformat; all 44 import statements pass. no dependency changes needed.
• risk/return models runs completely (8 code cells).
• the other four run up to their first Yahoo download, which times out (120s for notebooks 2/3, 30s for 4/5). later cells remain unverified.

notebooks 2, 4 and 5 already contain nonstandard jetTransient output fields. schema validation passes after clearing saved outputs in memory; those outputs are unchanged in this PR.

Closes #717

Supersedes #720 and #724 (both inactive for 5+ months with no maintainer feedback).
Supersedes #720 (inactive since March 2026).

assisted by Codex.