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/articles.html

@@ -168,7 +168,7 @@ const ArticlesApp = {
         getToken() { return localStorage.getItem('authToken'); },
         async api(url, opts = {}) {
             const token = this.getToken();
-            if (!token) { this.$message.error('请先登录'); setTimeout(() => window.location.href = '/', 1500); return null; }
+            if (!token) { this.$message.error('请先登录'); setTimeout(() => window.location.href = '/login.html', 1500); return null; }
             const res = await fetch(url, { headers: { 'Authorization': 'Bearer ' + token, 'Content-Type': 'application/json', ...opts.headers }, ...opts });
             if (!res.ok) { const data = await res.json().catch(() => ({})); throw new Error(data.detail || `请求失败: ${res.status}`); }
             return res.json();