fix: Auth redirects and navigation for landing page routing

- login.html: Post-login redirect / -> /index.html; already-logged-in redirect / -> /index.html
- articles.html, topics.html: Auth failure redirect -> /login.html
- uni-nav.js: Dashboard link / -> /index.html; navigate function fix for prefix handling
- sw.js: Remove / pre-cache; HTML documents use Network First strategy for fresh content

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

platform/frontend/login.html

@@ -103,7 +103,7 @@
                 type: 'success',
                 duration: 1500,
                 onClose: () => {
-                  window.location.href = '/';
+                  window.location.href = '/index.html';
                 }
               });
             } else {
@@ -120,7 +120,7 @@
         // 检查是否已登录
         const token = localStorage.getItem('authToken');
         if (token) {
-          window.location.href = '/';
+          window.location.href = '/index.html';
         }
 
         return {