Make CI enforcement trustworthy before the rules registry

[anth-volk]

Fixes #3886

Summary

Phase 0 of the rules workstream: make CI enforcement trustworthy before the rules registry (#3884, kept as a draft until this merges). The sim counterpart is PolicyEngine/policyengine-sim-api#754.

• CODEOWNERS (step 0.2). A deliberately narrow file covering only the rule machinery: rules/, scripts/rules/, scripts/guards/, scripts/run_quality_guards.py and CODEOWNERS itself, owned by @PolicyEngine/core-developers. pyproject.toml and workflow files are not owned, so dependency bots and everyday CI edits aren't blocked. The paths for the registry take effect once Add a rules registry that makes every enforced and unenforced rule visible #3884 creates them.
• Ruff pin (step 0.3). The lint jobs in pr.yml and push.yml ran pip install ruff>=0.9.0 unquoted, so the shell read > as a redirect and CI installed the latest ruff. They now run .github/scripts/install_locked_ruff.sh, which installs the version pinned in uv.lock (currently 0.15.12) and prints it. Following the workstream's CI rule, the multi-line logic lives in a tested script, and the workflow step is a single line. [tool.ruff.lint] select = ["E4", "E7", "E9", "F"] makes ruff's current defaults explicit. No rules are added or removed. Stricter ruff comes in separate PRs right after the registry lands.
• CRUD boundary discovery (step 0.5). test_data_crud_boundaries.py discovers modules by filename instead of listing them, so households and user_households (12 modules) are checked for the first time. Discovery fails at collection if a pattern matches nothing, because pytest silently skips an empty parameter list. A new test requires every connector module to be a recognised create, read, update or delete module.
• PR conventions (step 0.6) and the no-bypass rule. github-prs.md now requires a tracking issue and Fixes #ISSUE_NUMBER on the first line of the PR description, and a new PR template starts with that line. Agents must never bypass branch rules (for example gh pr merge --admin), even with admin credentials; AGENTS.md points to both.

Step 0.1 is not in this PR. It sets the required checks (Lint, Type-check API v2, Quality guards, Test) and turns on code-owner review in the main ruleset. That's a ruleset change, applied separately after merge.

Testing

• pytest tests/unit/v2/test_data_crud_boundaries.py: 40 tests pass, covering 39 discovered modules (previously 27) plus the classification test.
• Negative checks, each reverted afterwards:
  • Adding import sqlalchemy to services/v2/households/validators.py makes the households case fail. Before this change, nothing checked that module.
  • Adding a connector named writes.py makes the classification test fail.
• pytest tests/unit/test_install_locked_ruff_script.py: 4 tests pass, using fake pip and ruff. They cover the locked version, the repository's own lock as the default, a missing pin (fails without installing) and a failing pip. The script also passes shellcheck, and a real run against the repo's lock in a throwaway venv installs ruff 0.15.12.
• Ruff:
  • The install script reads 0.15.12 from the lock.
  • With that version, ruff format --check . and ruff check . both pass.
  • ruff check . with ruff 0.16.8 and the explicit select also passes. With 0.16.8's own defaults, it would report 867 errors.
• python scripts/run_quality_guards.py and tests/unit/test_alembic_skill.py pass.
• actionlint reports nothing on the changed workflows.
• GitHub's CODEOWNERS validation returns no errors for this branch.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.56%. Comparing base (21ddf34) to head (8cedb09).

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3887       +/-   ##
===========================================
+ Coverage   45.22%   87.56%   +42.33%     
===========================================
  Files         183      198       +15     
  Lines       11073    12211     +1138     
  Branches     1905     2159      +254     
===========================================
+ Hits         5008    10692     +5684     
+ Misses       5644      922     -4722     
- Partials      421      597      +176     

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