fix(deacon): use session package for hq- session names (gt-r38pj)

stale_hooks.go was using hardcoded 'gt-deacon' and 'gt-mayor' instead of
session.DeaconSessionName() and session.MayorSessionName() which return
'hq-deacon' and 'hq-mayor'. This caused incorrect session lookups.

Also fixes duplicate WorktreeAddFromRef method from merge conflict.

internal/deacon/stale_hooks.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/steveyegge/gastown/internal/session"
 	"github.com/steveyegge/gastown/internal/tmux"
 )
 
@@ -155,9 +156,9 @@ func assigneeToSessionName(assignee string) string {
 		// Simple names like "deacon", "mayor"
 		switch assignee {
 		case "deacon":
-			return "gt-deacon"
+			return session.DeaconSessionName()
 		case "mayor":
-			return "gt-mayor"
+			return session.MayorSessionName()
 		default:
 			return ""
 		}