test(fixtures): add test project with SVCs, tests, and reqstool status validation

[jimisola]

Summary

Adds tests/fixtures/test_project/ — a minimal Hatch project for end-to-end manual validation:

• pyproject.toml: hatchling build, reqstool hook config, pytest with junit XML output
• src/mypackage/main.py: @Requirements("REQ_001") on hello()
• tests/test_main.py: @SVCs("SVC_001") on test_hello()
• docs/reqstool/requirements.yml: REQ_001 (correct schema with metadata)
• docs/reqstool/software_verification_cases.yml: SVC_001 → REQ_001
• README.md: full 5-step validation guide including reqstool status

Note: unlike the poetry plugin, hatch injects reqstool_config.yml directly into the tarball
and does not bundle annotations.yml — the README documents the extra copy step needed for
reqstool status.

Test plan

• pytest tests/ --junit-xml=build/test-results/junit.xml passes
• hatch build adds reqstool_config.yml to tarball
• reqstool status shows REQ_001 implemented, T1 P1, no missing