feat: taskplane-style specs + CLI step tracking
- Triage agent generates full PROMPT.md (mission, steps, file scope,
review level, docs requirements, commit conventions, guardrails)
- Executor agent reports progress via hai task CLI
- hai task update <id> <step> <status> — step lifecycle
- hai task log <id> <message> — execution log
- hai task discover <id> <what> <disp> — record discoveries
- hai task show <id> — display steps, progress, discoveries, log
- Steps auto-parsed from PROMPT.md headings into task.json
- Task types extended with steps, reviews, discoveries, log
8a2a5ac14b