feat: opaque session、安装/发帖 SSR 与最小 Admin 后台

浏览器登录改为 DB sessions（可吊销）；敏感词与 OIDC PEM 入 settings；
落地安装向导、注册发帖与 /admin 仪表盘/板块/审核/设置。

Co-authored-by: Cursor <cursoragent@cursor.com>

templates/home/feed.tmpl

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+{{define "home/feed"}}
+<section class="j13-feed">
+  <header class="j13-feed__header">
+    <h1 class="j13-feed__title">{{if .BoardName}}{{.BoardName}}{{else}}全部帖子{{end}}</h1>
+    <div class="j13-sort" role="navigation" aria-label="排序">
+      <a class="{{if eq .Sort "latest"}}is-active{{end}}" href="{{sortURL .ActiveBoard "latest"}}">最新发帖</a>
+      <a class="{{if eq .Sort "reply"}}is-active{{end}}" href="{{sortURL .ActiveBoard "reply"}}">最新回复</a>
+      <a class="{{if eq .Sort "hot"}}is-active{{end}}" href="{{sortURL .ActiveBoard "hot"}}">热门讨论</a>
+    </div>
+  </header>
+  {{if not .Posts}}
+  <p class="j13-empty">暂无帖子。</p>
+  {{else}}
+  <ul class="j13-post-list">
+    {{range .Posts}}
+    <li class="j13-post-item">
+      <a class="j13-post-item__title" href="{{postURL .ID}}">{{.Title}}</a>
+      <div class="j13-post-item__meta">
+        {{if .Pinned}}<span class="j13-tag j13-tag--pin">置顶</span>{{end}}
+        {{if .Featured}}<span class="j13-tag j13-tag--feat">精华</span>{{end}}
+        {{if .BoardName}}<span class="j13-tag">{{.BoardName}}</span>{{end}}
+        <span>{{.AuthorName}}</span>
+        <span>{{.CreatedLabel}}</span>
+        <span>{{.CommentCount}} 回复</span>
+      </div>
+    </li>
+    {{end}}
+  </ul>
+  {{end}}
+  {{if or .HasPrev .HasMore}}
+  <nav class="j13-pager">
+    {{if .HasPrev}}<a href="{{pageURL .ActiveBoard .Sort .PrevPage}}">上一页</a>{{end}}
+    <span>第 {{.Page}} 页</span>
+    {{if .HasMore}}<a href="{{pageURL .ActiveBoard .Sort .NextPage}}">下一页</a>{{end}}
+  </nav>
+  {{end}}
+</section>
+{{end}}

templates/home/home.tmpl

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+{{define "home"}}
+{{template "base/head" .}}
+{{template "base/navbar" .}}
+{{if .Flash}}<div class="j13-flash" role="status">{{.Flash}}</div>{{end}}
+  <div class="j13-layout">
+    {{template "shared/board_aside" .}}
+    <main class="j13-main">
+      {{template "home/feed" .}}
+    </main>
+  </div>
+{{template "base/footer" .}}
+{{end}}