feat: implement AccessDeniedScreen and enhance error handling

- Introduced AccessDeniedScreen component for improved user experience when access is denied, replacing the previous AccessDenied component.
- Updated CurrentDutyView and CalendarPage to handle access denied scenarios, displaying the new screen appropriately.
- Enhanced tests for CurrentDutyView and AccessDeniedScreen to ensure correct rendering and functionality under access denied conditions.
- Refactored localization messages to include new labels for access denied scenarios in both English and Russian.

webapp-next/src/components/states/AccessDeniedScreen.tsx

@@ -0,0 +1,84 @@
+/**
+ * Full-screen access denied view. Used when the user is not allowed (no initData / not localhost)
+ * or when API returns 403. Matches global-error and not-found layout: no extra chrome, one action.
+ */
+
+"use client";
+
+import { useEffect } from "react";
+import { getLang, translate } from "@/i18n/messages";
+import { useAppStore } from "@/store/app-store";
+
+export interface AccessDeniedScreenProps {
+  /** Optional detail from API 403 response, shown below the hint. */
+  serverDetail?: string | null;
+  /** Primary button: reload (main page) or back/close (deep link). */
+  primaryAction: "reload" | "back";
+  /** Called when primaryAction is "back" (e.g. Back to calendar or Close). */
+  onBack?: () => void;
+  /** When true and primaryAction is "back", button label is "Close" instead of "Back to calendar". */
+  openedFromPin?: boolean;
+}
+
+/**
+ * Full-screen access denied: title, hint, optional server detail, single action button.
+ * Calls setAppContentReady(true) on mount so Telegram receives ready().
+ */
+export function AccessDeniedScreen({
+  serverDetail,
+  primaryAction,
+  onBack,
+  openedFromPin = false,
+}: AccessDeniedScreenProps) {
+  const lang = getLang();
+  const setAppContentReady = useAppStore((s) => s.setAppContentReady);
+
+  useEffect(() => {
+    setAppContentReady(true);
+  }, [setAppContentReady]);
+
+  const hasDetail = Boolean(serverDetail && String(serverDetail).trim());
+
+  const handleClick = () => {
+    if (primaryAction === "reload") {
+      if (typeof window !== "undefined") {
+        window.location.reload();
+      }
+    } else {
+      onBack?.();
+    }
+  };
+
+  const buttonLabel =
+    primaryAction === "reload"
+      ? translate(lang, "access_denied.reload")
+      : openedFromPin
+        ? translate(lang, "current_duty.close")
+        : translate(lang, "current_duty.back");
+
+  return (
+    <div
+      className="flex min-h-screen flex-col items-center justify-center gap-4 bg-background px-4 text-foreground"
+      role="alert"
+    >
+      <h1 className="text-xl font-semibold">
+        {translate(lang, "access_denied")}
+      </h1>
+      <p className="text-center text-muted-foreground">
+        {translate(lang, "access_denied.hint")}
+      </p>
+      {hasDetail && (
+        <p className="text-center text-sm text-muted-foreground">
+          {serverDetail}
+        </p>
+      )}
+      <button
+        type="button"
+        onClick={handleClick}
+        className="rounded-lg bg-primary px-4 py-2 text-primary-foreground hover:bg-primary/90"
+      >
+        {buttonLabel}
+      </button>
+    </div>
+  );
+}