docs: route validator operators to cathedral-validator

[wallscaler]

Outcome

Closes the legacy validator authority surface in cathedralai/cathedral.

• Routes validator installation, configuration, release, dry-run, broadcast, and runbook work to cathedralai/cathedral-validator.
• Removes the competing cathedral-validator and cathedral-thin-validator console scripts from this package.
• Marks retained validator configs, units, and dated launch material as mechanism-test or migration history.
• Preserves mechanism code and every systemd single-writer guard.

Evidence

• Focused repository and packaging checks: 7 passed, 2 warnings.
• Full intended local set: 154 passed, 2 warnings.
• Thin E2E: PASS, weight sum 1.0, attack cases rejected, retry deterministic.
• Ruff lint and format: PASS.
• Built wheel exposes neither validator console script.
• git diff --check: PASS.

The broader publisher/validator suite has 7 failed, 270 passed. The same seven failures reproduce on pristine base 4679d5e under Python 3.11.15 and are not introduced by this patch.

No deployment, service change, wallet access, or chain write is included.