fix: gardener migration — run-gardener.toml via direct cron, remove legacy scripts (#490)

Rewrite gardener-run.sh as direct cron runner (matching supervisor/planner/
predictor pattern): lock guard, memory check, worktree, tmux session with
Claude sonnet + formulas/run-gardener.toml, phase monitoring, cleanup.

- Delete gardener-poll.sh and gardener-agent.sh (superseded)
- Extract consume_escalation_reply() to lib/formula-session.sh (shared
  by gardener and supervisor, eliminates duplicate blocks)
- Update AGENTS.md, gardener/AGENTS.md, lib/AGENTS.md, CI smoke test,
  and cross-references

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -16,8 +16,7 @@ See `README.md` for the full architecture and `BOOTSTRAP.md` for setup.
 disinto/
 ├── dev/           dev-poll.sh, dev-agent.sh, phase-handler.sh — issue implementation
 ├── review/        review-poll.sh, review-pr.sh — PR review
-├── gardener/      gardener-run.sh — files action issue for run-gardener formula
-│                  gardener-poll.sh, gardener-agent.sh — grooming
+├── gardener/      gardener-run.sh — direct cron executor for run-gardener formula
 ├── predictor/     predictor-run.sh — daily cron executor for run-predictor formula
 ├── planner/       planner-run.sh — direct cron executor for run-planner formula
 │                  planner/journal/ — daily raw logs from each planner run