feat: 完善架构优化性能

- 调整音视频架构，提升 RKMPP 编码 MJPEG-->H264 性能，同时解决丢帧马赛克问题；
- 删除多用户逻辑，只保留单用户，支持设置 web 单会话；
- 修复删除体验不好的的回退逻辑，前端页面菜单位置微调；
- 增加 OTG USB 设备动态调整功能；
- 修复 mdns 问题，webrtc 视频切换更顺畅。

src/webrtc/mdns.rs

@@ -0,0 +1,34 @@
+use webrtc::ice::mdns::MulticastDnsMode;
+
+pub fn mdns_mode_from_env() -> Option<MulticastDnsMode> {
+    let raw = std::env::var("ONE_KVM_WEBRTC_MDNS_MODE").ok()?;
+    let value = raw.trim().to_ascii_lowercase();
+    if value.is_empty() {
+        return None;
+    }
+
+    match value.as_str() {
+        "disabled" | "off" | "false" | "0" => Some(MulticastDnsMode::Disabled),
+        "query" | "query_only" | "query-only" => Some(MulticastDnsMode::QueryOnly),
+        "gather" | "query_and_gather" | "query-and-gather" | "on" | "true" | "1" => {
+            Some(MulticastDnsMode::QueryAndGather)
+        }
+        _ => None,
+    }
+}
+
+pub fn mdns_mode() -> MulticastDnsMode {
+    mdns_mode_from_env().unwrap_or(MulticastDnsMode::QueryAndGather)
+}
+
+pub fn mdns_mode_label(mode: MulticastDnsMode) -> &'static str {
+    match mode {
+        MulticastDnsMode::Disabled => "disabled",
+        MulticastDnsMode::QueryOnly => "query_only",
+        MulticastDnsMode::QueryAndGather => "query_and_gather",
+    }
+}
+
+pub fn default_mdns_host_name(session_id: &str) -> String {
+    format!("{session_id}.local")
+}