chore: add engineering standards (dependabot)

[nikzen]

Automated rollout from engineering-standards.

Base (always included):

• .github/dependabot.yml – automated dependency updates (Dependabot)
• Ecosystems: github-actions, rust python
• Grouped PRs: major updates separate from minor+patch
• Cooldown: 14 days

Detected scope: rust python

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.13%. Comparing base (24f1cc4) to head (ed236bc).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #246      +/-   ##
==========================================
- Coverage   80.14%   80.13%   -0.01%     
==========================================
  Files         501      501              
  Lines       71549    71549              
  Branches    10751    10751              
==========================================
- Hits        57342    57337       -5     
- Misses      10947    10951       +4     
- Partials     3260     3261       +1     

see 3 files with indirect coverage changes

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