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/prime.go

@@ -19,6 +19,7 @@ import (
 	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/events"
 	"github.com/steveyegge/gastown/internal/lock"
+	"github.com/steveyegge/gastown/internal/session"
 	"github.com/steveyegge/gastown/internal/style"
 	"github.com/steveyegge/gastown/internal/templates"
 	"github.com/steveyegge/gastown/internal/workspace"
@@ -304,12 +305,18 @@ func outputPrimeContext(ctx RoleContext) error {
 	}
 
 	// Build template data
+	// Get town name for session names
+	townName, _ := workspace.GetTownName(ctx.TownRoot)
+
 	data := templates.RoleData{
-		Role:     roleName,
-		RigName:  ctx.Rig,
-		TownRoot: ctx.TownRoot,
-		WorkDir:  ctx.WorkDir,
-		Polecat:  ctx.Polecat,
+		Role:          roleName,
+		RigName:       ctx.Rig,
+		TownRoot:      ctx.TownRoot,
+		TownName:      townName,
+		WorkDir:       ctx.WorkDir,
+		Polecat:       ctx.Polecat,
+		MayorSession:  session.MayorSessionName(townName),
+		DeaconSession: session.DeaconSessionName(townName),
 	}
 
 	// Render and output