feat(validator): add HARD check for required files in organizations/<org>/

[justinmclean]

Summary

Add validate_organization_structure (check #16) that enforces every organizations// adapter directory contains README.md and organization.md. Clears the Known Gap in the organization-adapters spec: No structural validator check yet enforces required files in organizations// (currently README + organization.md by convention).

The check is HARD (ORGANIZATION_CATEGORY) so an incomplete adapter directory fails the validator rather than emitting only an advisory. The live tree (ASF/ and independent/) already carries both files, so no existing adapter is broken. The _template/ directory is excluded from the check, matching the existing known_organizations() convention.

8 new test cases in TestOrganizationStructure cover: well-formed org, missing README.md, missing organization.md, both files absent, template exclusion, multi-org sweep, empty organizations/ directory, and the HARD-category assertion. All 433 tests pass (uv run direct).

Generated-by: Claude (Opus 4.7)

Type of change

• Skill change (.claude/skills/<name>/) — eval fixtures updated below
• Tool / bridge contract (tools/<system>/*.md)
• Python package (tools/*/ with pyproject.toml)
• Groovy reference impl
• Cross-cutting (RFC, AGENTS.md, sandbox, privacy-LLM)
• Documentation (docs/, README.md, CONTRIBUTING.md)
• Project template (projects/_template/)
• CI / dev loop (prek, workflows, validators)
• Other:

Test plan

• prek run --all-files passes
• For Python packages touched: uv run pytest / ruff check / mypy passes
• For Groovy bridges touched: command-line invocation tested end-to-end
• For skill changes: eval suite passes for the affected skill
  (PYTHONPATH=tools/skill-evals/src python3 -m skill_evals.runner tools/skill-evals/evals/<skill>/)
• For skill behaviour changes: a new or updated eval fixture is included in this PR
  (a regression test for the bug fixed / the behaviour added — see CONTRIBUTING.md)
• Other:

[potiuk]

LGTM — adds validate_organization_structure() emitting a HARD organization violation when an organizations/<org>/ directory (excluding _template) lacks README.md or organization.md, wired into run_validation with 8 focused unit tests. The check matches the existing tree (all three live orgs pass, _template correctly excluded), reuses existing symbols, and adds no false positives. Not a skill change, so no eval suite is required. CI green.