agent: stale-lock start allows the benign LXC nesting WARNINGS advisory

Live on 9999: the recovery's start succeeded (guest running) but WaitTask
false-failed on "WARNINGS: 1" (the systemd-nesting notice). Mirror the
restore-test's start step (AllowWarnings) so a booted guest isn't logged
as a start error.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162BnMpUXscPsUB1cU8Tr6K

internal/localapi/stalelock.go

@@ -224,7 +224,10 @@ func (c *staleLockController) Start(ctx context.Context, vmid int) error {
 	if upid == "" {
 		return nil
 	}
-	_, err = c.px.WaitTask(ctx, upid, proxmox.WaitOptions{})
+	// AllowWarnings: an unprivileged LXC start emits a "WARNINGS: 1" advisory (the systemd-nesting
+	// notice) even when the guest boots fine — same as the restore-test's start step (task.go). Without
+	// this the recovery false-logs a start error for a guest that is actually up (seen live on 9999).
+	_, err = c.px.WaitTask(ctx, upid, proxmox.WaitOptions{AllowWarnings: true})
 	return err
 }