fix: 修复OTG gadget重建后HID后端未重载导致键鼠失效

当MSD或OTG网络配置变更导致gadget被重建时，新的/dev/hidg*设备
被创建但HID后端因'配置未变'跳过了reload，导致仍持有已删除设备
的旧文件描述符，键鼠操作无效。

修复: 在apply_usb_config中检测gadget是否因MSD/网络变更被重建，
若是且HID后端为OTG，强制reload HID以打开新的/dev/hidg*设备。

同时为MsdConfig添加PartialEq derive以支持变更检测。

src/config/schema/web.rs

@@ -44,7 +44,7 @@ impl Default for VideoConfig {
 }
 
 #[typeshare]
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(default)]
 pub struct MsdConfig {
     pub enabled: bool,

src/web/handlers/config/apply.rs

@@ -365,6 +365,10 @@ pub async fn apply_usb_config(
         let transitioning_away_from_otg =
             old_config.hid.backend == HidBackend::Otg && new_config.hid.backend != HidBackend::Otg;
 
+        let hid_unchanged = old_config.hid == new_config.hid;
+        let otg_gadget_rebuilt =
+            old_config.msd != new_config.msd || old_config.otg_network != new_config.otg_network;
+
         if transitioning_away_from_otg {
             apply_hid_config(
                 state,
@@ -394,6 +398,19 @@ pub async fn apply_usb_config(
             .await?;
         }
 
+        // When the OTG gadget was rebuilt due to MSD or network config changes
+        // while HID config stayed the same, the /dev/hidg* devices are new and
+        // the HID backend must be reloaded to reopen them.
+        if hid_unchanged && otg_gadget_rebuilt && new_config.hid.backend == HidBackend::Otg {
+            tracing::info!("OTG gadget rebuilt, reloading HID backend for new devices");
+            let hid_backend = hid_backend_type(&new_config.hid);
+            state
+                .hid
+                .reload(hid_backend)
+                .await
+                .map_err(|e| AppError::Config(format!("HID reload after gadget rebuild failed: {}", e)))?;
+        }
+
         apply_msd_config(
             state,
             &old_config.msd,