feat(search): 按参考稿重做搜索框并支持后台配置

- 顶部悬浮引擎标签 + 下拉选项，使用 stash-ui 新增的 EngineIcon
- 站内搜索保持现有本地过滤与回车打开首个匹配项
- 外部引擎使用配置的 {query} 模板新标签页搜索
- settings 新增 search.default / search.engines，后台新增『搜索框』配置默认项、名称、地址与启停
- 默认默认搜索项为站内搜索，地址校验必须含 {query}

src/db/settings.rs

@@ -119,6 +119,64 @@ pub struct BackgroundSettings {
     pub dark: String,
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, Default)]
+#[serde(default)]
+pub struct SearchEngineSettings {
+    pub id: String,
+    pub name: String,
+    /// 搜索地址模板，用 `{query}` 表示关键词
+    pub url: String,
+    pub enabled: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(default)]
+pub struct SearchSettings {
+    /// `internal` 或某个引擎 id
+    pub default: String,
+    pub engines: Vec<SearchEngineSettings>,
+}
+
+impl Default for SearchSettings {
+    fn default() -> Self {
+        Self {
+            default: "internal".into(),
+            engines: vec![
+                SearchEngineSettings {
+                    id: "google".into(),
+                    name: "Google".into(),
+                    url: "https://www.google.com/search?q={query}".into(),
+                    enabled: true,
+                },
+                SearchEngineSettings {
+                    id: "bing".into(),
+                    name: "Bing".into(),
+                    url: "https://www.bing.com/search?q={query}".into(),
+                    enabled: true,
+                },
+                SearchEngineSettings {
+                    id: "baidu".into(),
+                    name: "百度".into(),
+                    url: "https://www.baidu.com/s?wd={query}".into(),
+                    enabled: true,
+                },
+                SearchEngineSettings {
+                    id: "sogou".into(),
+                    name: "搜狗".into(),
+                    url: "https://www.sogou.com/web?query={query}".into(),
+                    enabled: true,
+                },
+                SearchEngineSettings {
+                    id: "360".into(),
+                    name: "360".into(),
+                    url: "https://www.so.com/s?q={query}".into(),
+                    enabled: true,
+                },
+            ],
+        }
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 #[serde(default)]
 pub struct ProfileSettings {
@@ -230,6 +288,7 @@ pub struct Settings {
     pub header: HeaderSettings,
     pub sidebar: SidebarSettings,
     pub background: BackgroundSettings,
+    pub search: SearchSettings,
     pub profile: ProfileSettings,
     pub site: SiteMetaSettings,
 }
@@ -295,6 +354,46 @@ pub fn validate(settings: &Settings) -> Result<(), StashError> {
             "暗色背景地址最多 500 个字符".into(),
         ));
     }
+    if settings.search.engines.len() > 10 {
+        return Err(StashError::InvalidDirectory("搜索引擎最多 10 个".into()));
+    }
+    let mut ids = std::collections::HashSet::new();
+    for engine in &settings.search.engines {
+        if !matches!(
+            engine.id.as_str(),
+            "google" | "bing" | "baidu" | "sogou" | "360"
+        ) {
+            return Err(StashError::InvalidDirectory("搜索引擎标识不合法".into()));
+        }
+        if !ids.insert(engine.id.as_str()) {
+            return Err(StashError::InvalidDirectory("搜索引擎标识不能重复".into()));
+        }
+        let name = engine.name.trim();
+        if name.is_empty() || name.chars().count() > 20 {
+            return Err(StashError::InvalidDirectory("搜索引擎名称需为 1–20 个字".into()));
+        }
+        let url = engine.url.trim();
+        if url.chars().count() > 500
+            || !(url.starts_with("http://") || url.starts_with("https://"))
+            || !url.contains("{query}")
+        {
+            return Err(StashError::InvalidDirectory(
+                "搜索地址需以 http(s):// 开头并包含 {query}".into(),
+            ));
+        }
+    }
+    let default = settings.search.default.trim();
+    if default != "internal" {
+        let engine = settings
+            .search
+            .engines
+            .iter()
+            .find(|engine| engine.id == default)
+            .ok_or_else(|| StashError::InvalidDirectory("默认搜索引擎不存在".into()))?;
+        if !engine.enabled {
+            return Err(StashError::InvalidDirectory("默认搜索引擎未启用".into()));
+        }
+    }
     if settings.site.title.chars().count() > 120 {
         return Err(StashError::InvalidDirectory("页面标题最多 120 个字".into()));
     }