Introduce thread_state_ledger_validator for the mandatory two-comment
workflow: tagged [CONTROLLER HANDOFF] paired with [THREAD STATE LEDGER].
Wire validation into final_report_validator and gitea_create_issue_comment,
add runbook docs, worked examples, and tests.
Closes#507
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
