Fix Poetry package declarations for validation SDK

[skamanbo]

Summary

• remove invalid top-level Poetry package declarations for ai_validation, ai_validation_service, and ai_defense
• retain aidefense as the package root, which recursively includes the generated validation subpackages

Root cause

The validation modules are located under aidefense/pydantic/validation/, but pyproject.toml declared them as top-level package directories. poetry install --extras aibom therefore failed with ai_validation does not contain any element before tests could run.

Impact

This restores dependency installation and package building for the 2.1.3 release branch without changing runtime behavior.

Validation

• poetry check — passed with existing deprecation warnings
• poetry install --extras aibom — passed
• poetry build — passed; generated validation modules are present in the wheel
• git diff --check — passed
• poetry run pytest — 596 passed, 8 skipped, 3 pre-existing failures in aidefense/tests/test_config.py related to singleton warning behavior removed by the base branch