Add JSDoc documentation and file headers to all source files

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

postcss.config.cjs

@@ -1,3 +1,13 @@
+// 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), 2026/3/6
+/**
+ * @module postcss.config
+ *   PostCSS configuration with Tailwind CSS plugin.
+ */
+
 module.exports = {
   plugins: {
     "@tailwindcss/postcss": {},