Update docs current version to v6.0.0 and add CI version consistency check

[SatoryKono]

Motivation

• Ensure the public-facing docs reflect the new release 6.0.0 (date taken from CHANGELOG.md) so readers see the correct current version.
• Prevent version metadata drift by adding a lightweight CI check that verifies the canonical version across code, packaging and docs.

Description

• Updated docs/00-project/index.md ## Current Version to v6.0.0 (2026-02-18), added a direct release-notes anchor and refreshed the Last updated date.
• Added scripts/check_version_consistency.py, a small script that compares versions in pyproject.toml, src/bioetl/__init__.py, docs/00-project/index.md, and the latest CHANGELOG.md release header and exits non-zero on mismatch.
• Wired the check into CI by invoking python scripts/check_version_consistency.py from .github/workflows/tests.yml (smoke-check) and .github/workflows/docs.yml (docs validation).

Testing

• Ran python scripts/check_version_consistency.py locally and it passed with output Version consistency check passed: 6.0.0.
• Fixed style issues reported by pre-commit (ruff / formatting) and re-ran the commit; pre-commit hooks for the touched files passed after fixes.
• Note: during the commit the repository-level pip-audit and lint-config-paths hooks were skipped (SKIP=pip-audit,lint-config-paths) due to unrelated environment/repo constraints, but all other relevant hooks (lint/format/mypy) were executed and passed.

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