Phase 3-4: Goals AI planner, Team tasks, Push notifications, i18n (CZ/HE/RU/UA)

- Goals CRUD API + AI study plan generator + progress reports
- Goals frontend page with progress bars
- Team tasks: assign, transfer, collaborate endpoints
- Push notifications: web-push, VAPID, subscribe/send
- i18n: 4 languages (cs, he, ru, ua) translation files
- notifications.js + goals.js routes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/tasks/lib/i18n.tsx

@@ -0,0 +1,99 @@
+"use client";
+
+import { createContext, useContext, useState, useEffect, useCallback, ReactNode } from "react";
+
+import cs from "@/messages/cs.json";
+import he from "@/messages/he.json";
+import ru from "@/messages/ru.json";
+import ua from "@/messages/ua.json";
+
+export type Locale = "cs" | "he" | "ru" | "ua";
+
+export const LOCALES: { code: Locale; label: string; flag: string; dir: "ltr" | "rtl" }[] = [
+  { code: "cs", label: "\u010ce\u0161tina", flag: "\ud83c\udde8\ud83c\uddff", dir: "ltr" },
+  { code: "he", label: "\u05e2\u05d1\u05e8\u05d9\u05ea", flag: "\ud83c\uddee\ud83c\uddf1", dir: "rtl" },
+  { code: "ru", label: "\u0420\u0443\u0441\u0441\u043a\u0438\u0439", flag: "\ud83c\uddf7\ud83c\uddfa", dir: "ltr" },
+  { code: "ua", label: "\u0423\u043a\u0440\u0430\u0457\u043d\u0441\u044c\u043a\u0430", flag: "\ud83c\uddfa\ud83c\udde6", dir: "ltr" },
+];
+
+type Messages = typeof cs;
+
+const MESSAGES: Record<Locale, Messages> = { cs, he, ru, ua };
+
+const STORAGE_KEY = "taskteam_language";
+
+function getNestedValue(obj: unknown, path: string): string {
+  const keys = path.split(".");
+  let current: unknown = obj;
+  for (const key of keys) {
+    if (current == null || typeof current !== "object") return path;
+    current = (current as Record<string, unknown>)[key];
+  }
+  return typeof current === "string" ? current : path;
+}
+
+interface I18nContextType {
+  locale: Locale;
+  setLocale: (locale: Locale) => void;
+  t: (key: string) => string;
+  dir: "ltr" | "rtl";
+  isRTL: boolean;
+}
+
+const I18nContext = createContext<I18nContextType>({
+  locale: "cs",
+  setLocale: () => {},
+  t: (key: string) => key,
+  dir: "ltr",
+  isRTL: false,
+});
+
+export function useTranslation() {
+  return useContext(I18nContext);
+}
+
+export function I18nProvider({ children }: { children: ReactNode }) {
+  const [locale, setLocaleState] = useState<Locale>("cs");
+  const [mounted, setMounted] = useState(false);
+
+  useEffect(() => {
+    setMounted(true);
+    if (typeof window !== "undefined") {
+      const stored = localStorage.getItem(STORAGE_KEY) as Locale | null;
+      if (stored && MESSAGES[stored]) {
+        setLocaleState(stored);
+      }
+    }
+  }, []);
+
+  const setLocale = useCallback((newLocale: Locale) => {
+    setLocaleState(newLocale);
+    if (typeof window !== "undefined") {
+      localStorage.setItem(STORAGE_KEY, newLocale);
+    }
+  }, []);
+
+  const t = useCallback(
+    (key: string): string => {
+      return getNestedValue(MESSAGES[locale], key);
+    },
+    [locale]
+  );
+
+  const localeInfo = LOCALES.find((l) => l.code === locale) || LOCALES[0];
+  const dir = localeInfo.dir;
+  const isRTL = dir === "rtl";
+
+  // Update html attributes when locale changes
+  useEffect(() => {
+    if (!mounted) return;
+    document.documentElement.lang = locale;
+    document.documentElement.dir = dir;
+  }, [locale, dir, mounted]);
+
+  return (
+    <I18nContext.Provider value={{ locale, setLocale, t, dir, isRTL }}>
+      {children}
+    </I18nContext.Provider>
+  );
+}