feat(write-path): guard megameetings and unknown facets at event write time
Add a facet-registry gate in hooks.py that consults get_facets() once per write call and skips events with unknown or non-canonical facets with a WARNING log.
Add a megameeting guard in occurrence.py that rejects meeting events with more than 25 participants with a WARNING log.
Tighten the meetings.md and timeline.md prompts so orgs, projects, tools, and topics are not lifted into structured participants.
Document the existing muted-facet silent-disable behavior in docs/JOURNAL.md for agents such as entity_observer.
Add 8 focused tests in tests/test_output_hooks.py and prepend the worktree root in tests/conftest.py so pytest exercises local code.
Defensive guards against pollution patterns surfaced in the CPO journal-data-quality investigation.
Co-Authored-By: OpenAI Codex <codex@openai.com>