feat: use hq- prefix for Mayor and Deacon session names

Town-level services (Mayor, Deacon) now use hq- prefix instead of gt-:
- hq-mayor (was gt-mayor)
- hq-deacon (was gt-deacon)

This distinguishes town-level sessions from rig-level sessions which
continue to use gt- prefix (gt-gastown-witness, gt-gastown-crew-max, etc).

Changes:
- session.MayorSessionName() returns "hq-mayor"
- session.DeaconSessionName() returns "hq-deacon"
- ParseSessionName() handles both hq- and gt- prefixes
- categorizeSession() handles both prefixes
- categorizeSessions() accepts both prefixes
- Updated all tests and documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/agents.go

@@ -127,24 +127,29 @@ func init() {
 
 // categorizeSession determines the agent type from a session name.
 func categorizeSession(name string) *AgentSession {
-	// Must start with gt- prefix
+	session := &AgentSession{Name: name}
+
+	// Town-level agents use hq- prefix: hq-mayor, hq-deacon
+	if strings.HasPrefix(name, "hq-") {
+		suffix := strings.TrimPrefix(name, "hq-")
+		if suffix == "mayor" {
+			session.Type = AgentMayor
+			return session
+		}
+		if suffix == "deacon" {
+			session.Type = AgentDeacon
+			return session
+		}
+		return nil // Unknown hq- session
+	}
+
+	// Rig-level agents use gt- prefix
 	if !strings.HasPrefix(name, "gt-") {
 		return nil
 	}
 
-	session := &AgentSession{Name: name}
 	suffix := strings.TrimPrefix(name, "gt-")
 
-	// Town-level agents: gt-mayor, gt-deacon (simple format, one per machine)
-	if suffix == "mayor" {
-		session.Type = AgentMayor
-		return session
-	}
-	if suffix == "deacon" {
-		session.Type = AgentDeacon
-		return session
-	}
-
 	// Witness sessions: legacy format gt-witness-<rig> (fallback)
 	if strings.HasPrefix(suffix, "witness-") {
 		session.Type = AgentWitness