feat(i18n): install react-i18next, create English locale files, and initialize i18n framework

- Install i18next, react-i18next, i18next-browser-languagedetector
- Create 6 namespace JSON files (common, collection, threads, setups, onboarding, settings)
- Initialize i18n with language detection (localStorage + navigator)
- Wire i18n import in main.tsx before React rendering

Phase 34, Plan 01

src/client/main.tsx

@@ -1,3 +1,4 @@
+import "./lib/i18n";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { createRouter, RouterProvider } from "@tanstack/react-router";
 import { StrictMode } from "react";