fix(kanban): require verifier evidence for worker completion

[camaragon]

Summary

• require verifier evidence before dispatcher-owned worker tasks can complete
• record auditable completion_blocked_weak_verification events on weak closes
• update kanban_complete guidance/errors so workers provide metadata.verification.checks

Verification

• python -m pytest tests/hermes_cli/test_kanban_core_functionality.py tests/hermes_cli/test_kanban_cli.py tests/tools/test_kanban_tools.py tests/hermes_cli/test_kanban_db.py -q -o 'addopts=' → 286 passed, 2 warnings
• git diff --check → clean
• python -m py_compile hermes_cli/kanban.py hermes_cli/kanban_db.py tools/kanban_tools.py tests/hermes_cli/test_kanban_db.py tests/hermes_cli/test_kanban_core_functionality.py tests/tools/test_kanban_tools.py → clean
• simple diff secret scan → 0 matches

Notes

• Stacked after fix(kanban): gate autonomous dispatch by governance headers #21914 governance dispatch gates. If fix(kanban): gate autonomous dispatch by governance headers #21914 is not merged yet, this PR includes that parent commit in the compare view.

[teknium1]

Thanks @camaragon — closing this one. The PR proposes a substantive policy: dispatcher-spawned worker tasks would be blocked from completing without a metadata.verification.checks field, with auditable completion_blocked_weak_verification events on weak closes.

This is a behavioral policy decision that's bigger than a mechanical salvage:

• It changes the worker completion contract — every existing kanban worker prompt and skill would need updates to know it must populate the verification metadata, or completions would start failing.
• Stacked on top of fix(kanban): gate autonomous dispatch by governance headers #21914 (governance dispatch gates) which is itself not merged.
• 442 LOC across 20+ files including auth, doctor, codex_app_server, gateway, kanban — too cross-cutting to salvage without deciding the underlying policy first.

If verifier-gated completion is something we want to add, it deserves a focused, narrow PR against current main with the policy boundaries clearly specified (which tasks does it apply to, what counts as 'evidence', what's the migration story for existing workers). Appreciate the careful design work.