feat: 链路控制、延迟校准与长测工具，补全文档

- 固件：新增 link_control / stream_control，覆盖运行中 Wi-Fi 断线恢复、取帧节拍、
  温控与质量/帧率减载；UDP 发送增加有界重试预算与帧期限，PSRAM JPEG 直发减少拷贝。
- 协议：重组器严格校验分片布局，统计未收齐、超时与完全缺失的帧，处理帧号回绕与设备重启。
- 桌面端：视频改 latest-value 通道并前置帧时间标记，拒绝积压和慢解码的过期画面；新增
  延迟标记页与 --latency-report 校准，完善录制、服务端与退出流程。
- 文档与脚本：新增硬件、开发、延迟、功耗、实时性、稳定性文档和改动记录，重写根 README；
  新增构建、性能、延迟与串口长测脚本，以及长测客户端脚本。
- 构建：固定 esp-1.97.0.0 工具链，分区表随构建复制，更新 sdkconfig 与忽略规则。

desktop/core/Cargo.lock

@@ -55,6 +55,7 @@ dependencies = [
  "rand",
  "serde",
  "serde_json",
+ "socket2",
  "toml",
 ]
 
@@ -297,6 +298,16 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "socket2"
+version = "0.6.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d1e2c7f27f8d4cb10542a02c49005dbd6e93095799d6f3be745fae9f8fedd4"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
 [[package]]
 name = "subtle"
 version = "2.6.1"
@@ -391,6 +402,21 @@ dependencies = [
  "wit-bindgen",
 ]
 
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "winnow"
 version = "0.7.15"