Run ruff check in CI with the first group of rule families

[anth-volk]

Fixes #3897

Summary

Phase 1 step 1.8, group 1 of about 8: safe auto-fixes. Stacked on #3896.

• ruff check . now runs in CI (lint job in pr.yml and push.yml), using the ruff version pinned in uv.lock.
• New rule families: select gains FLY, FURB, I, PIE, PYI, RET, RSE, UP and W. Every finding is fixed, with no ratchet. About 620 were ruff's safe fixes (mostly import sorting and pyupgrade); the rest are below.
• Fixed by hand:
  • Nine v2 model enums move from (str, Enum) to StrEnum (UP042). None is formatted with str() or format(). SQLAlchemy and Pydantic store and serialise them by value, and their repr is unchanged.
  • RET504 and PIE810 fixes reviewed. compare_economic_outputs now returns None explicitly. Two __enter__ methods return Self.
  • Import sorting wrapped two long imports and moved their # type: ignore onto the wrong line. They're back on the import line, and mypy passes.
• Alembic revisions: they're now exempt from all lint rules (previously F401 only). They must stay exactly as Alembic generates them (api.migration.alembic-autogenerated-only), and the revision tests check that. The hand-written env.py files are still linted.
• Registry: api.quality.ruff-lint moves from advisory to enforced.

Testing

• pytest tests/unit tests/contract: 2,358 passed.
• mypy: no issues (97 files).
• ruff check . passes with 0.15.12 (pinned) and 0.16.8. ruff format --check . passes.
• All quality guards pass. Rules tool unittest: 75 pass.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 94.63602% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.56%. Comparing base (0ff411d) to head (f1871e7).

Files with missing lines	Patch %	Lines
policyengine_api/services/economy_comparison.py	20.00%	4 Missing and 4 partials ⚠️
policyengine_api/fastapi_routes/dependencies.py	25.00%	2 Missing and 1 partial ⚠️
policyengine_api/services/report_output_service.py	75.00%	1 Missing ⚠️
...engine_api/services/v2/metadata/transformations.py	66.66%	1 Missing ⚠️
policyengine_api/utils/singleton.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##           ci-scripts-deploy    #3898   +/-   ##
==================================================
  Coverage              87.56%   87.56%           
==================================================
  Files                    198      198           
  Lines                  12211    12208    -3     
  Branches                2159     2159           
==================================================
- Hits                   10692    10690    -2     
+ Misses                   922      921    -1     
  Partials                 597      597           

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