fix: Remove escalation — planner routes through vault instead (#721)

Remove ESCALATED signal and escalation handling from planner, supervisor,
and gardener. When blocked on external resources or human decisions, these
agents now file vault procurement items (vault/pending/*.md) instead of
escalating directly to the human.

Changes:
- Planner formula: ESCALATED signal replaced with HUMAN_BLOCKED; files
  vault items and marks prerequisites as blocked-on-vault
- Supervisor formula/prompt: escalation sections replaced with vault item
  filing; preflight now reports pending vault items instead of escalation
  replies
- Gardener formula: ESCALATE action replaced with VAULT action; files
  vault/pending/*.md for human decisions
- Groom-backlog formula: same ESCALATE→VAULT replacement
- Gardener shell: PHASE:escalate replaced with PHASE:failed for merge
  blocks and CI exhaustion; escalation reply consumption removed
- Supervisor shell: escalation reply consumption removed from both
  supervisor-run.sh and legacy supervisor-poll.sh
- Prerequisite tree: #466 updated from "escalated" to "blocked-on-vault"

The vault is the factory's only interface to the human for resources and
approvals. Dev/action agents retain PHASE:escalate for operational session
issues (CI timeouts, merge blocks) which are a different mechanism.

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

supervisor/preflight.sh

@@ -214,14 +214,15 @@ else
 fi
 echo ""
 
-# ── Escalation Replies from Matrix ────────────────────────────────────────
+# ── Pending Vault Items ───────────────────────────────────────────────────
 
-echo "## Escalation Replies (from Matrix)"
-if [ -s /tmp/supervisor-escalation-reply ]; then
-  cat /tmp/supervisor-escalation-reply
-  echo ""
-  echo "(Reply already consumed by supervisor-run.sh before this session)"
-else
-  echo "  None"
-fi
+echo "## Pending Vault Items"
+_found_vault=false
+for _vf in "${PROJECT_REPO_ROOT}/vault/pending/"*.md; do
+  [ -f "$_vf" ] || continue
+  _found_vault=true
+  _vtitle=$(grep -m1 '^# ' "$_vf" | sed 's/^# //' || basename "$_vf")
+  echo "  $(basename "$_vf"): ${_vtitle}"
+done
+[ "$_found_vault" = false ] && echo "  None"
 echo ""