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/daemon/lifecycle.go

@@ -12,7 +12,9 @@ import (
 	"github.com/steveyegge/gastown/internal/beads"
 	"github.com/steveyegge/gastown/internal/config"
 	"github.com/steveyegge/gastown/internal/constants"
+	"github.com/steveyegge/gastown/internal/session"
 	"github.com/steveyegge/gastown/internal/tmux"
+	"github.com/steveyegge/gastown/internal/workspace"
 )
 
 // BeadsMessage represents a message from gt mail inbox --json.
@@ -310,8 +312,16 @@ func (d *Daemon) identityToSession(identity string) string {
 
 	// Fallback: use default patterns based on role type
 	switch parsed.RoleType {
-	case "mayor", "deacon":
-		return "gt-" + parsed.RoleType
+	case "mayor":
+		if townName, err := workspace.GetTownName(d.config.TownRoot); err == nil {
+			return session.MayorSessionName(townName)
+		}
+		return ""
+	case "deacon":
+		if townName, err := workspace.GetTownName(d.config.TownRoot); err == nil {
+			return session.DeaconSessionName(townName)
+		}
+		return ""
 	case "witness", "refinery":
 		return fmt.Sprintf("gt-%s-%s", parsed.RigName, parsed.RoleType)
 	case "crew":