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.

site/docs/architecture.html

@@ -431,9 +431,9 @@
           <td>Review-agent injects feedback</td>
         </tr>
         <tr>
-          <td>needs_human</td>
-          <td>Blocked on a human decision</td>
-          <td>Matrix notification sent</td>
+          <td>escalate</td>
+          <td>Needs human input (any reason)</td>
+          <td>Matrix notification sent; 24h timeout → blocked</td>
         </tr>
         <tr>
           <td>done</td>