Add JSDoc documentation and file headers to all source files

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/i18n/i18n.js

@@ -1,3 +1,14 @@
+// The Lucia project.
+// Copyright 2023-2026 DSP, inc.  All rights reserved.
+// Authors:
+//   chiayin.kuo@dsp.im (chiayin), 2023/1/31
+//   imacat.yang@dsp.im (imacat), 2023/9/23
+//   cindy.chang@dsp.im (Cindy Chang), 2024/5/30
+/**
+ * @module i18n Internationalization configuration using i18next
+ *   with browser language detection.
+ */
+
 import i18next from 'i18next';
 import LanguageDetector from 'i18next-browser-languagedetector';
 import enLocale from './en.json';