skills: add meeting-debrief community skill

[Aryan4443]

What this is

A community skill: skills/community/meeting-debrief/SKILL.md. Markdown only, no Python, no new dependencies.

meeting-prep covers walking into a meeting. Nothing covered walking out of one and the decisions and commitments made on a call are both the facts most worth landing in memory and the ones that evaporate fastest.

How it behaves

Find the meeting with list_events, ask one open question, sort the answer into four buckets (Decided / I owe / They owe / Open), and show the card before writing anything so the user can correct it while it is still text.

Only then does it write:

• save_note — one call per durable fact, subject being the person or project. Facts, not narration.
• create_event — only for commitments that carry a date, titled as the action rather than the meeting.
• send_message — offered, not assumed.
• manage_memory — only when the meeting made an existing memory wrong; search first for the id.

Edge cases cover the short answer ("it was fine"), a cancelled meeting, a decision that contradicts memory, vague dates, several meetings at once, and the user who is venting rather than reporting.

Checks

• python scripts/validate_skills.py → OK, 4 skills
• python -m ruff check waku evals scripts → All checks passed
• python scripts/generate_env_example.py --check → clean
• python -m pytest -q evals/deterministic → 615 passed, 60 skipped
• Body is 49 lines, inside the 80-line budget