Add PyPI wheel packaging smoke test for bundled registry skills (#182).

[rosspeili]

Summary

Adds a wheel-smoke CI job that validates the PyPI shipping path: build a wheel, install it in a fresh venv (base deps only — no [all] or per-skill extras), and verify every bundled registry skill via scripts/wheel_smoke_test.py.

SkillLoader.load_skill() gains check_requirements=False so the smoke test can load bundles for packaging checks without installing optional skill extras.

Refs #182

What changed

• scripts/wheel_smoke_test.py — checks bundle files, manifest/name parity, instructions/card assets; loads skills where possible; defers skills that need optional extras (expected)
• .github/workflows/ci.yml — new wheel-smoke job (existing build job unchanged)
• skillware/core/loader.py — check_requirements: bool = True kwarg
• tests/test_loader.py — coverage for check_requirements=False
• Docs — TESTING.md, CONTRIBUTING.md, ai_native_workflow.md
• .flake8 / .gitignore — exclude local .venv-wheel-smoke/ test venv

Type of change

• Framework Feature — SkillLoader.check_requirements
• Packaging — wheel smoke test for bundled skills
• RFC / meta — CI workflow

Checklist

• Linked issue (Refs #182)
• Scope matches the issue — no unrelated refactors
• black --check and flake8 pass locally
• pytest skills/ and pytest tests/ pass locally (266 passed)
• CHANGELOG.md updated under [Unreleased]
• examples/README.md — N/A
• test_registry_docs.py — N/A (no skill/catalog changes)

Test plan

• python -m black --check .
• python -m flake8 .
• python -m pytest skills/ tests/
• Build wheel + scripts/wheel_smoke_test.py locally (10 loaded, 3 deferred)
• Confirm wheel-smoke job passes on GitHub Actions

Related issues

Refs #182