feat(hid): 支持 CH9329 + OTG 组合模式

CH9329 负责键鼠，OTG 提供虚拟媒体、USB 网络和音频；分别配置设备、报告运行状态，并在 OTG 配置变更和回滚时保留未变化的 CH9329 实例。

补齐双设备校验、串口冲突检查、初始化引导和功能入口，修复组合模式下鼠标兼容选项缺失。

验证：独立功能版本的 591 项 Rust 库测试、前端生产构建、3 项引导逻辑测试及 2 组浏览器回归通过。未进行目标 KVM 硬件验证。

src/hid/backend.rs

@@ -37,6 +37,27 @@ pub enum HidBackendType {
     None,
 }
 
+impl From<&crate::config::HidConfig> for HidBackendType {
+    fn from(config: &crate::config::HidConfig) -> Self {
+        use crate::config::HidBackend;
+        match config.backend {
+            HidBackend::Otg => Self::Otg {
+                macos_drag: config.mouse_macos_drag,
+            },
+            HidBackend::Ch9329 | HidBackend::Ch9329Otg => Self::Ch9329 {
+                port: config.ch9329_port.clone(),
+                baud_rate: config.ch9329_baudrate,
+                hybrid_mouse: config.ch9329_hybrid_mouse,
+                macos_drag: config.mouse_macos_drag,
+            },
+            HidBackend::Bluetooth => Self::Bluetooth {
+                config: config.bluetooth.clone(),
+            },
+            HidBackend::None => Self::None,
+        }
+    }
+}
+
 impl HidBackendType {
     pub fn name_str(&self) -> &str {
         match self {

src/hid/mod.rs

@@ -767,6 +767,60 @@ fn merge_pending_move(pending: &mut Option<MouseEvent>, event: MouseEvent) {
 #[cfg(test)]
 mod queue_tests {
     use super::*;
+    #[cfg(unix)]
+    #[tokio::test]
+    async fn composite_otg_updates_and_rollback_preserve_hid_instance() {
+        let mut old = crate::config::AppConfig::default();
+        old.hid.backend = crate::config::HidBackend::Ch9329;
+        old.enforce_invariants();
+        let otg = Arc::new(OtgService::new());
+        let controller = Arc::new(HidController::new(
+            HidBackendType::from(&old.hid),
+            Some(otg.clone()),
+        ));
+        let pressed = Arc::new(AtomicBool::new(true));
+        let (runtime, _) = tokio::sync::watch::channel(());
+        let backend: Arc<dyn HidBackend> = Arc::new(TestBackend {
+            pressed: pressed.clone(),
+            reset_done: Arc::new(tokio::sync::Notify::new()),
+            runtime,
+        });
+        *controller.backend.write().await = Some(backend.clone());
+        let data = tempfile::tempdir().unwrap();
+        let coordinator = crate::runtime::UsbCoordinator::new(
+            controller.clone(),
+            otg,
+            Arc::new(RwLock::new(None)),
+            Arc::new(RwLock::new(None)),
+            Arc::new(EventBus::new()),
+            data.path().into(),
+        );
+        let mut new = old.clone();
+        new.hid.backend = crate::config::HidBackend::Ch9329Otg;
+        new.hid.otg_udc = Some("test.udc".into());
+        new.hid.otg_descriptor.product = "Advanced USB".into();
+        new.hid.otg_keyboard_leds = true;
+        coordinator.apply_config(&old, &new).await.unwrap();
+        assert!(Arc::ptr_eq(
+            controller.backend.read().await.as_ref().unwrap(),
+            &backend
+        ));
+        coordinator.apply_config(&new, &old).await.unwrap();
+        assert!(Arc::ptr_eq(
+            controller.backend.read().await.as_ref().unwrap(),
+            &backend
+        ));
+        assert!(pressed.load(Ordering::Acquire));
+        // Invalid OTG configuration must not touch the healthy input backend.
+        new.uac.enabled = true;
+        new.uac.sample_rate = 8000;
+        assert!(coordinator.apply_config(&old, &new).await.is_err());
+        assert!(Arc::ptr_eq(
+            controller.backend.read().await.as_ref().unwrap(),
+            &backend
+        ));
+    }
+
     #[tokio::test]
     async fn screen_resolution_updates_backend_and_retains_valid_dimensions() {
         #[cfg(unix)]