fix: remove dead code (toast stubs, unused Redis key, tunnel manager fields)

- Remove 7 no-op exported stubs from toast.tsx (ToastProvider, ToastViewport,
  Toast, ToastTitle, ToastDescription, ToastClose, useToasts) — nothing imports them
- Remove fwFailKey variable and its Set() call from worker.go — the
  firmware:check-failed Redis key was never read anywhere
- Remove unused deviceStore and credCache fields from tunnel.Manager struct
  and drop corresponding parameters from NewManager(); update call site in
  main.go and all test usages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

poller/cmd/poller/main.go

@@ -196,8 +196,6 @@ func main() {
 		cfg.TunnelPortMin,
 		cfg.TunnelPortMax,
 		time.Duration(cfg.TunnelIdleTimeout)*time.Second,
-		deviceStore,
-		credentialCache,
 	)
 	defer tunnelMgr.Shutdown()
 	slog.Info("tunnel manager initialized",