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

models/setting.go

@@ -0,0 +1,55 @@
+package models
+
+import (
+	"database/sql"
+	"fmt"
+
+	"simple_portal/database"
+)
+
+// Predefined search engine URL templates.
+const (
+	SearchEngineGoogle = "https://www.google.com/search?q=%s"
+	SearchEngineBing   = "https://www.bing.com/search?q=%s"
+	SearchEngineBaidu  = "https://www.baidu.com/s?wd=%s"
+)
+
+// SettingKey constants.
+const (
+	SettingKeySearchEngine      = "search_engine"
+	SettingKeyHomepageTitle     = "homepage_title"
+	SettingKeyHomepageSubtitle  = "homepage_subtitle"
+	SettingKeyHomepageBackground = "homepage_background"
+)
+
+// Default setting values.
+const (
+	DefaultHomepageTitle     = "Portal"
+	DefaultHomepageSubtitle  = ""
+	DefaultHomepageBackground = ""
+)
+
+// GetSetting retrieves a setting value by key. Returns empty string if not found.
+func GetSetting(key string) (string, error) {
+	var value sql.NullString
+	err := database.DB.QueryRow("SELECT value FROM settings WHERE key = ?", key).Scan(&value)
+	if err == sql.ErrNoRows {
+		return "", nil
+	}
+	if err != nil {
+		return "", fmt.Errorf("failed to get setting %s: %w", key, err)
+	}
+	return value.String, nil
+}
+
+// SetSetting inserts or updates a setting value by key.
+func SetSetting(key, value string) error {
+	_, err := database.DB.Exec(
+		"INSERT INTO settings (key, value) VALUES (?, ?) ON CONFLICT(key) DO UPDATE SET value = ?",
+		key, value, value,
+	)
+	if err != nil {
+		return fmt.Errorf("failed to set setting %s: %w", key, err)
+	}
+	return nil
+}