refactor: update lifecycle mail targets from daemon/ to deacon/ (gt-5af.5)

Update all code and documentation to use deacon/ instead of daemon/
for lifecycle mail targets:

- internal/cmd/handoff.go: getManager() returns deacon/ for Mayor/Witness
- internal/daemon/lifecycle.go: ProcessLifecycleRequests uses deacon/ inbox
- docs/architecture.md: update all references in lifecycle docs
- scripts/mayor-respawn-daemon.sh: use BD_IDENTITY=deacon for mail commands

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/architecture.md

@@ -808,7 +808,7 @@ Workers process issues independently. Work flows through the merge queue. No "sw
 Gas Town Daemon (gt daemon)
 ├── Pokes Mayor periodically
 ├── Pokes all Witnesses periodically
-├── Processes lifecycle requests from daemon/ inbox
+├── Processes lifecycle requests from deacon/ inbox
 └── Restarts sessions when cycle requested
 
 Lifecycle Hierarchy:
@@ -834,8 +834,8 @@ gt handoff --restart    # Fresh restart, no handoff
 |-------|---------|------------------|
 | Polecat | --shutdown | rig/witness |
 | Refinery | --cycle | rig/witness |
-| Witness | --cycle | daemon/ |
-| Mayor | --cycle | daemon/ |
+| Witness | --cycle | deacon/ |
+| Mayor | --cycle | deacon/ |
 
 **Lifecycle request protocol**:
 1. Agent runs `gt handoff` (verifies git clean, sends handoff mail)
@@ -851,7 +851,7 @@ gt handoff --restart    # Fresh restart, no handoff
 - Poke Mayor: "HEARTBEAT: check your rigs"
 - Poke each Witness: "HEARTBEAT: check your workers"
 - Agents ignore poke if already working
-- Process any lifecycle requests in daemon/ inbox
+- Process any lifecycle requests in deacon/ inbox
 - Restart dead sessions if cycle was requested
 
 ```mermaid