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.

planner/prerequisite-tree.md

@@ -28,8 +28,8 @@ Status: BLOCKED — prerequisite of prerequisite unresolved
 Status: BLOCKED — prerequisite chain unresolved
 
 ## Objective: Unified escalation path (#510)
-- [ ] Supervisor escalates prolonged needs_human (#465)
-Status: BLOCKED — 1 prerequisite unresolved
+- [x] PHASE:escalate replaces PHASE:needs_human (supersedes #465)
+Status: IN PROGRESS
 
 ## Objective: Vault as procurement gate + RESOURCES.md inventory (#504)
 - [x] RESOURCES.md exists