feat: enforce RESULT.json completion protocol as Iron Law in taskMaestro

[JeremyDev87]

Purpose

Workers occasionally complete their work but fail to write RESULT.json, leaving the conductor unable to detect completion. The completion protocol should be elevated to an Iron Law — non-negotiable, always enforced.

Changes

• .claude/skills/taskmaestro/SKILL.md — Add Iron Law section for completion protocol
• Worker prompt template — Strengthen RESULT.json instruction priority

Expected Behavior

Iron Law: RESULT.json MUST be the LAST action before idle.

Worker completion sequence:
  1. Complete implementation
  2. Create PR via /ship
  3. Write RESULT.json ← MANDATORY, before anything else
  4. Go idle

If /ship fails:
  1. Write RESULT.json with status: "failure"
  2. Include error details
  3. Go idle

Acceptance Criteria

• Iron Law section added to taskMaestro SKILL.md
• Worker prompt template includes RESULT.json as non-negotiable final step
• Failure case covered: write RESULT.json even on /ship failure
• Watch mode can distinguish "completed without RESULT.json" from "still working"
• Can be merged independently

References

• Incident: 2026-03-22 Wave 2 pane 2 (feat(skills): add tmux-master skill for expert tmux operations #804) — completed but no RESULT.json
• Incident: 2026-03-22 Wave 3 pane 3 (feat(mcp): add teams execution strategy to dispatch_agents #807) — PR not created, no RESULT.json
• Parent: Improve taskMaestro parallel execution reliability (retrospective action items) #866