fix: read clash mode tolerantly and propagate mode-switch failures

The home mode card read the proxy mode only from mihomo's /configs (strict
BaseConfig); when that response drifted a single field, the whole read
failed and the card showed a bare "communication error". patch_clash_mode
also swallowed backend PATCH failures and always returned Ok, so the UI
could not tell a switch had actually failed.

- add a tolerant get_clash_mode command that reads mode from the saved
  clash config (IClashTemp::get_mode), bypassing strict BaseConfig
  deserialization, and
- make change_clash_mode return Result and have patch_clash_mode propagate
  it; the hotkey/tray callers log-and-ignore as before.

src-tauri/src/config/clash.rs

@@ -180,6 +180,17 @@ impl IClashTemp {
             }),
         }
     }
+
+    /// 容错读取当前代理模式。
+    ///
+    /// 仅从已保存的 clash 配置 Mapping 中提取 `mode` 字段，不依赖 mihomo `/configs`
+    /// 的严格 `BaseConfig` 反序列化，因此即使核心返回的字段与插件结构体不匹配也能取到。
+    pub fn get_mode(&self) -> Option<String> {
+        self.0.get("mode").and_then(|value| match value {
+            Value::String(val_str) => Some(val_str.clone()),
+            _ => None,
+        })
+    }
     #[cfg(not(target_os = "windows"))]
     pub fn guard_redir_port(config: &Mapping) -> u16 {
         let mut port = config