refactor(js): app.js 를 브라우저 네이티브 ESM 모듈로 분할

public/js/{util,ui,reactions,modals,comments,feed,main}.js 로 분리하고
dashboard/project 에서 <script type="module" src="/public/js/main.js"> 로 로드.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

views/dashboard.ejs

@@ -241,6 +241,6 @@
   </div>
 </div>
 
-<script src="/public/app.js"></script>
+<script type="module" src="/public/js/main.js"></script>
 </body>
 </html>

views/project.ejs

@@ -6,6 +6,6 @@
     </div>
   </div>
 </main>
-<script src="/public/app.js"></script>
+<script type="module" src="/public/js/main.js"></script>
 </body>
 </html>