feat(i18n): add multi-language UI support with 5 languages

- Add i18n framework with locale detection and cookie persistence
- Support English, Traditional Chinese (zh-TW), Simplified Chinese (zh-CN), Japanese (ja), Korean (ko)
- Add LanguageSelector component in navigation header
- Create locale JSON files with full translations
- Update all page components (root, user, results, history) with i18n support
- Add client-side translation helpers for dynamic content
- Auto-detect user's preferred language from browser settings
- Bump version to v0.1.3

src/i18n/service.ts

@@ -0,0 +1,44 @@
+import { Elysia, t } from "elysia";
+import {
+  type SupportedLocale,
+  createTranslator,
+  defaultLocale,
+  detectLocale,
+  getLocale,
+} from "../i18n";
+
+/**
+ * Elysia plugin for i18n/locale handling
+ * Adds locale detection and translator to the context
+ */
+export const localeService = new Elysia({ name: "locale/service" })
+  .model({
+    localeSession: t.Cookie({
+      locale: t.Optional(t.String()),
+    }),
+  })
+  .derive({ as: "global" }, ({ cookie, request }) => {
+    // Get locale from cookie or detect from Accept-Language header
+    const cookieLocale = cookie.locale?.value;
+    const acceptLanguage = request.headers.get("accept-language") ?? undefined;
+
+    let locale: SupportedLocale;
+
+    if (cookieLocale) {
+      locale = getLocale(cookieLocale);
+    } else {
+      locale = detectLocale(acceptLanguage);
+    }
+
+    const t = createTranslator(locale);
+
+    return {
+      locale,
+      t,
+    };
+  });
+
+export type LocaleContext = {
+  locale: SupportedLocale;
+  t: ReturnType<typeof createTranslator>;
+};