Fix cost recording for hq-* tmux sessions

detectCurrentTmuxSession() was only accepting gt-* prefix sessions,
rejecting town-level sessions like hq-mayor. Now accepts both gt-*
and hq-* prefixes.

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

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

internal/cmd/costs.go

@@ -679,7 +679,8 @@ func detectCurrentTmuxSession() string {
 
 	session := strings.TrimSpace(string(output))
 	// Only return if it looks like a Gas Town session
-	if strings.HasPrefix(session, constants.SessionPrefix) {
+	// Accept both gt- (rig sessions) and hq- (town-level sessions like hq-mayor)
+	if strings.HasPrefix(session, constants.SessionPrefix) || strings.HasPrefix(session, constants.HQSessionPrefix) {
 		return session
 	}
 	return ""