feat(web): integrate localized application catalogs

- compose app, UI, and independently imported block catalogs from JSON configuration\n- persist the selected locale on the server and activate it without hydration flicker\n- add a flag-based language switcher and localized navigation descriptors\n- mount the redesigned i18n devtool only in development\n- regenerate English and Simplified Chinese catalogs and add switcher coverage

apps/web/src/server/app-locale.functions.ts

@@ -0,0 +1,20 @@
+import { createServerFn } from "@tanstack/react-start"
+
+import { isAppLocale } from "@/i18n/app-locales"
+import { readAppLocale, writeAppLocale } from "./app-locale.server"
+
+export const getAppLocale = createServerFn({ method: "GET" }).handler(() => {
+  return readAppLocale()
+})
+
+export const setAppLocale = createServerFn({ method: "POST" })
+  .validator((value: unknown) => {
+    if (!isAppLocale(value)) {
+      throw new Error("Invalid app locale")
+    }
+
+    return value
+  })
+  .handler(({ data }) => {
+    writeAppLocale(data)
+  })

apps/web/src/server/app-locale.server.ts

@@ -0,0 +1,25 @@
+import "@tanstack/react-start/server-only"
+import { getCookie, setCookie } from "@tanstack/react-start/server"
+
+import {
+  DEFAULT_APP_LOCALE,
+  isAppLocale,
+  type AppLocale,
+} from "@/i18n/app-locales"
+
+const APP_LOCALE_COOKIE = "ui-locale"
+const COOKIE_MAX_AGE = 60 * 60 * 24 * 365
+
+export function readAppLocale(): AppLocale {
+  const locale = getCookie(APP_LOCALE_COOKIE)
+
+  return isAppLocale(locale) ? locale : DEFAULT_APP_LOCALE
+}
+
+export function writeAppLocale(locale: AppLocale) {
+  setCookie(APP_LOCALE_COOKIE, locale, {
+    maxAge: COOKIE_MAX_AGE,
+    path: "/",
+    sameSite: "lax",
+  })
+}