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/supervisor-run.sh

@@ -59,9 +59,6 @@ else
   log "WARNING: preflight.sh failed, continuing with partial data"
 fi
 
-# ── Consume escalation replies ────────────────────────────────────────────
-consume_escalation_reply "supervisor"
-
 # ── Load formula + context ───────────────────────────────────────────────
 load_formula "$FACTORY_ROOT/formulas/run-supervisor.toml"
 build_context_block AGENTS.md
@@ -77,16 +74,11 @@ build_prompt_footer
 PROMPT="You are the supervisor agent for ${FORGE_REPO}. Work through the formula below. You MUST write PHASE:done to '${PHASE_FILE}' when finished — the orchestrator will time you out if you return to the prompt without signalling.
 
 You have full shell access and --dangerously-skip-permissions.
-Fix what you can. Escalate what you cannot. Do NOT ask permission — act first, report after.
+Fix what you can. File vault items for what you cannot. Do NOT ask permission — act first, report after.
 
 ## Pre-flight metrics (collected $(date -u +%H:%M) UTC)
 ${PREFLIGHT_OUTPUT}
-${ESCALATION_REPLY:+
-## Escalation Reply (from Matrix — human message)
-${ESCALATION_REPLY}
 
-Act on this reply in the decide-actions step.
-}
 ## Project context
 ${CONTEXT_BLOCK}
 ${SCRATCH_CONTEXT:+${SCRATCH_CONTEXT}