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.

review/review-poll.sh

@@ -156,7 +156,7 @@ curl -sf -X PATCH \\
 echo \"PHASE:done\" > \"${phase_file}\"
 
 If merge fails due to conflicts, rebase first then retry.
-If merge repeatedly fails, write PHASE:needs_human."
+If merge repeatedly fails, write PHASE:escalate with a reason."
   elif [ "${verdict}" = "REQUEST_CHANGES" ] || [ "${verdict}" = "DISCUSS" ]; then
     inject_msg="Review: ${verdict} on PR #${pr_num}: