feat: 门户网站初始提交

- Go + Gin + html/template 服务端渲染
- 主页：Google 风格搜索框 + 导航卡片
- 后台：卡片 CRUD、搜索引擎配置、主页背景/标题配置
- 图片上传：支持 jpg/jpeg/png/gif，自动压缩，缩略图参数 ?thumb=1
- 安全：登录日志、修改密码、IP 自动封禁、IP 白名单
- 访问统计：主页访问/卡片点击/搜索追踪、实时流量、IP 统计
- SQLite 存储（modernc.org/sqlite，纯 Go）
- 内存 Session + bcrypt 密码哈希

templates/admin/settings.html

@@ -0,0 +1,80 @@
+{{define "admin/settings.html"}}
+{{template "header" .}}
+<div class="admin-layout">
+    <nav class="admin-nav">
+        <div class="admin-nav-brand">Portal 管理</div>
+        <div class="admin-nav-links">
+            <a href="/admin" class="admin-nav-link">首页</a>
+            <a href="/admin/cards" class="admin-nav-link">卡片管理</a>
+            <a href="/admin/access-logs" class="admin-nav-link">访问日志</a>
+            <a href="/admin/logs" class="admin-nav-link">登录日志</a>
+            <a href="/admin/ip-whitelist" class="admin-nav-link">IP白名单</a>
+            <a href="/admin/settings" class="admin-nav-link active">设置</a>
+            <a href="/admin/password" class="admin-nav-link">修改密码</a>
+        </div>
+        <div class="admin-nav-user">
+            <span>{{.Username}}</span>
+            <form method="POST" action="/admin/logout" style="display:inline">
+                <button type="submit" class="btn btn-sm btn-secondary">退出</button>
+            </form>
+        </div>
+    </nav>
+    <main class="admin-main">
+        <h1>设置</h1>
+
+        {{if .Error}}<div class="form-error">{{.Error}}</div>{{end}}
+        {{if .Message}}<div class="form-success">{{.Message}}</div>{{end}}
+
+        <form method="POST" action="/admin/settings" class="admin-form">
+            <h2 class="form-section-title">搜索引擎</h2>
+            <div class="form-group">
+                <label for="search_engine">默认搜索引擎</label>
+                <select id="search_engine" name="search_engine">
+                    {{range $name, $url := .Engines}}
+                    <option value="{{$url}}" {{if eq $url $.SearchEngine}}selected{{end}}>{{$name}}</option>
+                    {{end}}
+                </select>
+            </div>
+            <div class="form-group">
+                <label>当前引擎 URL</label>
+                <input type="text" value="{{.SearchEngine}}" readonly class="input-readonly">
+            </div>
+            <div class="form-group">
+                <label for="custom_url">自定义搜索引擎 URL（需包含 %s 作为搜索词占位符）</label>
+                <input type="url" id="custom_url" name="custom_url" placeholder="https://example.com/search?q=%s">
+            </div>
+
+            <h2 class="form-section-title">主页配置</h2>
+            <div class="form-group">
+                <label for="homepage_title">主页标题</label>
+                <input type="text" id="homepage_title" name="homepage_title" value="{{.HomepageTitle}}" placeholder="Portal">
+            </div>
+            <div class="form-group">
+                <label for="homepage_subtitle">主页副标题</label>
+                <input type="text" id="homepage_subtitle" name="homepage_subtitle" value="{{.HomepageSubtitle}}" placeholder="快速导航，一键直达">
+            </div>
+            <div class="form-group">
+                <label for="homepage_background">主页背景图片 URL</label>
+                <input type="text" id="homepage_background" name="homepage_background" value="{{.HomepageBackground}}" placeholder="留空则使用默认渐变色">
+                {{if .HomepageBackground}}
+                <div class="background-preview">
+                    <img src="{{.HomepageBackground}}?thumb=1" alt="背景预览" class="upload-preview-img">
+                    <a href="{{.HomepageBackground}}" target="_blank" class="preview-link">查看原图</a>
+                </div>
+                {{end}}
+            </div>
+
+            <div class="form-actions">
+                <button type="submit" class="btn btn-primary">保存设置</button>
+            </div>
+        </form>
+    </main>
+</div>
+<script src="/static/upload.js"></script>
+<script>
+document.addEventListener('DOMContentLoaded', function() {
+    setupUpload('#homepage_background', 'background');
+});
+</script>
+{{template "footer" .}}
+{{end}}