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/constants/constants.go

@@ -89,11 +89,15 @@ const (
 )
 
 // Tmux session names.
-// Mayor and Deacon use simple session names: gt-mayor, gt-deacon (one per machine).
+// Mayor and Deacon use hq- prefix: hq-mayor, hq-deacon (town-level, one per machine).
+// Rig-level services use gt- prefix: gt-<rig>-witness, gt-<rig>-refinery, etc.
 // Use session.MayorSessionName() and session.DeaconSessionName().
 const (
-	// SessionPrefix is the prefix for all Gas Town tmux sessions.
+	// SessionPrefix is the prefix for rig-level Gas Town tmux sessions.
 	SessionPrefix = "gt-"
+
+	// HQSessionPrefix is the prefix for town-level services (Mayor, Deacon).
+	HQSessionPrefix = "hq-"
 )
 
 // Agent role names.