fix: Make Mayor/Deacon session names include town name

Session names `gt-mayor` and `gt-deacon` were hardcoded, causing tmux
session name collisions when running multiple towns simultaneously.

Changed to `gt-{town}-mayor` and `gt-{town}-deacon` format (e.g.,
`gt-ai-mayor`) to allow concurrent multi-town operation.

Key changes:
- session.MayorSessionName() and DeaconSessionName() now take townName param
- Added workspace.GetTownName() helper to load town name from config
- Updated all callers in cmd/, daemon/, doctor/, mail/, rig/, templates/
- Updated tests with new session name format
- Bead IDs remain unchanged (already scoped by .beads/ directory)

Fixes #60

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

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

internal/cmd/dog.go

@@ -483,10 +483,13 @@ func showDogStatus(mgr *dog.Manager, name string) error {
 	// Check for tmux session
 	townRoot, _ := workspace.FindFromCwd()
 	if townRoot != "" {
-		sessionName := fmt.Sprintf("gt-deacon-%s", name)
-		tm := tmux.NewTmux()
-		if has, _ := tm.HasSession(sessionName); has {
-			fmt.Printf("\nSession: %s (running)\n", sessionName)
+		townName, err := workspace.GetTownName(townRoot)
+		if err == nil {
+			sessionName := fmt.Sprintf("gt-%s-deacon-%s", townName, name)
+			tm := tmux.NewTmux()
+			if has, _ := tm.HasSession(sessionName); has {
+				fmt.Printf("\nSession: %s (running)\n", sessionName)
+			}
 		}
 	}