Standard .gitignore baseline should exclude Python bytecode (__pycache__/, *.pyc)

[don-petry]

Problem

The org baseline .gitignore (seeded into repos from repo-template) does not exclude Python bytecode. When an agent workflow runs the test suite and then commits the working tree, it silently commits compiled bytecode.

Observed concretely: in petry-projects/incubator#121, dev-lead ran pytest while fixing review comments and committed 11 __pycache__/*.pyc files (pocs/demand-radar/__pycache__/*.cpython-312.pyc and the pytest-cache .pycs under tests/__pycache__/). No reviewer or agent caught it because it's the agent's own byproduct, and nothing in .gitignore prevents it.

This will recur on any Python-touching repo where an agent (or a human running tests) commits broadly — bytecode is non-deterministic noise that bloats diffs and can leak local paths/versions.

Proposal

Add Python bytecode patterns to the standard baseline .gitignore (and/or the backend-python / fullstack stack variants under standards/):

# Python bytecode & caches
__pycache__/
*.py[cod]
.pytest_cache/

Rationale:

• __pycache__/ + *.py[cod] covers .pyc/.pyo/.pyd.
• .pytest_cache/ covers pytest's own cache dir.
• These are universally safe to ignore (always regenerable), so seeding them fleet-wide has no downside.

Acceptance

• Baseline .gitignore (and Python stack variants) include the patterns above.
• A fresh repo from repo-template no longer lets a pytest run's bytecode be committed.

Filed from work on petry-projects/incubator#121, where the gap surfaced.