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- Delete gardener-poll.sh and gardener-agent.sh (superseded)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>

.woodpecker/agent-smoke.sh

@@ -192,8 +192,6 @@ check_script dev/dev-agent.sh          dev/phase-handler.sh
 check_script dev/phase-handler.sh      dev/dev-agent.sh lib/secret-scan.sh
 check_script dev/dev-poll.sh
 check_script dev/phase-test.sh
-check_script gardener/gardener-agent.sh  lib/agent-session.sh
-check_script gardener/gardener-poll.sh
 check_script gardener/gardener-run.sh
 check_script review/review-pr.sh
 check_script review/review-poll.sh