fix: correct SQLAlchemy compatibility and verify packaged quickstarts

[svalench]

Summary

• Require SQLAlchemy 2.0+, matching the existing implementation: 1.4.54 satisfied the old metadata but failed to import.
• Include missing test fixtures, configuration, and example documentation in the sdist.
• Execute five actual README/docs quickstarts in isolated processes, covering CRUD and OpenAPI.
• Add installed-wheel CI and correct version checks in the legacy publishing workflows to use pyproject.toml.
• Clarify installation/run instructions and ignore generated local artifacts.

Verification

• Python 3.12 / SQLAlchemy 2.0.0: 258 passed, 41 unchanged skips; coverage 73.26%.
• Installed wheel: 3 sync examples passed without aiosqlite; all 5 passed with it.
• Extracted sdist: 9 selected tests passed.
• Build, strict Twine, strict MkDocs, and 10 version-guard cases passed.
• New test passes Ruff; 1,717 pre-existing full-project findings remain, with none introduced.

No runtime refactor, version bump, release, or package publication. Optional ORM adapters and other Python versions await GitHub CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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