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- Delete gardener-poll.sh and gardener-agent.sh (superseded)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

supervisor/supervisor-run.sh

@@ -57,16 +57,7 @@ else
 fi
 
 # ── Consume escalation replies ────────────────────────────────────────────
-# Move the file atomically so matrix_listener can write a new one
-ESCALATION_REPLY=""
-if [ -s /tmp/supervisor-escalation-reply ]; then
-  _reply_tmp="/tmp/supervisor-escalation-reply.consumed.$$"
-  if mv /tmp/supervisor-escalation-reply "$_reply_tmp" 2>/dev/null; then
-    ESCALATION_REPLY=$(cat "$_reply_tmp")
-    rm -f "$_reply_tmp"
-    log "Consumed escalation reply: $(echo "$ESCALATION_REPLY" | head -1)"
-  fi
-fi
+consume_escalation_reply "supervisor"
 
 # ── Load formula + context ───────────────────────────────────────────────
 load_formula "$FACTORY_ROOT/formulas/run-supervisor.toml"