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/rig/manager.go

@@ -14,6 +14,7 @@ import (
 	"github.com/steveyegge/gastown/internal/config"
 	"github.com/steveyegge/gastown/internal/git"
 	"github.com/steveyegge/gastown/internal/templates"
+	"github.com/steveyegge/gastown/internal/workspace"
 )
 
 // Common errors
@@ -794,12 +795,18 @@ func (m *Manager) createRoleCLAUDEmd(workspacePath string, role string, rigName
 		return err
 	}
 
+	// Get town name for session names
+	townName, _ := workspace.GetTownName(m.townRoot)
+
 	data := templates.RoleData{
-		Role:     role,
-		RigName:  rigName,
-		TownRoot: m.townRoot,
-		WorkDir:  workspacePath,
-		Polecat:  workerName, // Used for crew member name as well
+		Role:          role,
+		RigName:       rigName,
+		TownRoot:      m.townRoot,
+		TownName:      townName,
+		WorkDir:       workspacePath,
+		Polecat:       workerName, // Used for crew member name as well
+		MayorSession:  fmt.Sprintf("gt-%s-mayor", townName),
+		DeaconSession: fmt.Sprintf("gt-%s-deacon", townName),
 	}
 
 	content, err := tmpl.RenderRole(role, data)