Clean up stale issue references in comments (gt-z5bri)

- daemon.go: Update gt-2hzl4 comment to past tense (timeout fallback is implemented)
- lifecycle.go: Remove "to be removed" promise for gt-psuw7 (code stays)
- keepalive_test.go: Remove tombstoned gt-gaxo epic reference
- doctor.go: Remove tombstoned gt-gaxo epic reference
- daemon_test.go: Remove tombstoned gt-gaxo epic reference

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

internal/daemon/lifecycle.go

@@ -171,7 +171,7 @@ func (d *Daemon) executeLifecycleAction(request *LifecycleRequest) error {
 		}
 	}
 
-	// Check if session exists (legacy tmux detection - to be removed per gt-psuw7)
+	// Check if session exists (tmux detection still needed for lifecycle actions)
 	running, err := d.tmux.HasSession(sessionName)
 	if err != nil {
 		return fmt.Errorf("checking session: %w", err)