fix: feat: unified escalation — single PHASE:escalate path for all agents (#510)

Replace PHASE:needs_human with PHASE:escalate across all agent types.
Consolidates 6 overlapping escalation mechanisms into one unified path:
detect → notify via Matrix → session stays alive → human reply injected → resume.

Key changes:
- PHASE:escalate replaces PHASE:needs_human everywhere (16 files)
- CI exhausted now escalates instead of immediately marking blocked
- Matrix listener routes free-text replies to vault tmux sessions
- Vault agent writes PHASE:escalate files for procurement requests
- Supervisor monitors PHASE:escalate sessions in health checks
- 24h timeout on escalation → blocked label + session killed
- All 38 phase protocol tests updated and passing

Supersedes #462, #458, #465.

lib/formula-session.sh

@@ -168,7 +168,7 @@ formula_phase_callback() {
         log "ERROR: could not restart session after crash"
       fi
       ;;
-    PHASE:done|PHASE:failed|PHASE:needs_human|PHASE:merged)
+    PHASE:done|PHASE:failed|PHASE:escalate|PHASE:merged)
       agent_kill_session "${_MONITOR_SESSION:-$SESSION_NAME}"
       ;;
   esac