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/up.go

@@ -79,20 +79,24 @@ func runUp(cmd *cobra.Command, args []string) error {
 		}
 	}
 
+	// Get session names
+	deaconSession, _ := getDeaconSessionName()
+	mayorSession, _ := getMayorSessionName()
+
 	// 2. Deacon (Claude agent)
-	if err := ensureSession(t, DeaconSessionName, townRoot, "deacon"); err != nil {
+	if err := ensureSession(t, deaconSession, townRoot, "deacon"); err != nil {
 		printStatus("Deacon", false, err.Error())
 		allOK = false
 	} else {
-		printStatus("Deacon", true, "gt-deacon")
+		printStatus("Deacon", true, deaconSession)
 	}
 
 	// 3. Mayor (Claude agent)
-	if err := ensureSession(t, MayorSessionName, townRoot, "mayor"); err != nil {
+	if err := ensureSession(t, mayorSession, townRoot, "mayor"); err != nil {
 		printStatus("Mayor", false, err.Error())
 		allOK = false
 	} else {
-		printStatus("Mayor", true, "gt-mayor")
+		printStatus("Mayor", true, mayorSession)
 	}
 
 	// 4. Witnesses (one per rig)