fix(ui): correct i18next type augmentation scope and client boundary

- src/i18n/types.d.ts had no import/export, so its declare module block was
  an ambient module declaration shadowing the whole i18next package instead
  of an augmentation. This resolved allowObjectInHTMLChildren against a
  broken module, widened HTMLAttributes children to include
  Record<string, unknown>, and broke unrelated components (combobox, dialog,
  dropdown-menu, sheet, tooltip) plus i18next named imports. Adding a top
  level import turns it into a proper augmentation.
- src/i18n/index.ts barrel now has use client; importing it from a server
  layout evaluated react-i18next's context-creating module scope in the
  server graph and failed page data collection with createContext is not
  a function

ui/litellm-dashboard/src/i18n/index.ts

@@ -0,0 +1,10 @@
+"use client";
+
+// ./i18n.ts imports react-i18next, whose module scope calls React context APIs.
+// Without this directive, importing the barrel from a server component (e.g.
+// app/layout.tsx) evaluates that module in the server graph and the build fails
+// with "createContext is not a function".
+export { I18nProvider, useI18n } from "./I18nProvider";
+export { getI18n } from "./i18n";
+export type { Locale } from "./resources/registry";
+export { supportedLngs, NAMESPACES } from "./resources/registry";

ui/litellm-dashboard/src/i18n/types.d.ts

@@ -0,0 +1,23 @@
+/**
+ * Global i18next type augmentation. This file is owned by Agent 4 permanently.
+ */
+// This import makes this file a module, which turns `declare module` below into
+// an augmentation instead of an ambient declaration that would shadow the whole
+// i18next package's types.
+import "i18next";
+
+declare module "i18next" {
+  interface CustomTypeOptions {
+    defaultNS: "common";
+    // Deliberately NO strict `resources` key augmentation here. i18next v26's
+    // typed qualified keys are fragile (colons stripped in the union, qualified
+    // non-default lookups typed `unknown`, resource-shape sensitivity) and, in
+    // this static-export dashboard, repeatedly broke `next build`'s type check
+    // for a benefit that is redundant with the guarantees we already have:
+    //   - runtime key correctness is enforced by the readiness gate (ADR-03,
+    //     no raw-key flash) and
+    //   - en/zh key inventory is enforced by A7's check-keys CI gate.
+    // So keys are typed loosely (`string`), which compiles stably. Common-NS
+    // keys are still used unprefixed per `defaultNS`.
+  }
+}