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/templates/templates.go

@@ -24,14 +24,17 @@ type Templates struct {
 
 // RoleData contains information for rendering role contexts.
 type RoleData struct {
-	Role        string   // mayor, witness, refinery, polecat, crew, deacon
-	RigName     string   // e.g., "greenplace"
-	TownRoot    string   // e.g., "/Users/steve/ai"
-	WorkDir     string   // current working directory
-	Polecat     string   // polecat name (for polecat role)
-	Polecats    []string // list of polecats (for witness role)
-	BeadsDir    string   // BEADS_DIR path
-	IssuePrefix string   // beads issue prefix
+	Role           string   // mayor, witness, refinery, polecat, crew, deacon
+	RigName        string   // e.g., "greenplace"
+	TownRoot       string   // e.g., "/Users/steve/ai"
+	TownName       string   // e.g., "ai" - the town identifier for session names
+	WorkDir        string   // current working directory
+	Polecat        string   // polecat name (for polecat role)
+	Polecats       []string // list of polecats (for witness role)
+	BeadsDir       string   // BEADS_DIR path
+	IssuePrefix    string   // beads issue prefix
+	MayorSession   string   // e.g., "gt-ai-mayor" - dynamic mayor session name
+	DeaconSession  string   // e.g., "gt-ai-deacon" - dynamic deacon session name
 }
 
 // SpawnData contains information for spawn assignment messages.