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。

scripts/build.sh

@@ -1,14 +1,18 @@
 #!/usr/bin/env bash
 # Builds the firmware with the credentials from .env (see .env.example).
 #
-# ESP-IDF location comes from .cargo/config.toml (IDF_PATH /
-# ESP_IDF_TOOLS_INSTALL_DIR), so no ESP-IDF activation is needed here as long as
-# those point at an installation you already have. Drop them to let esp-idf-sys
-# fetch its own pinned ESP-IDF.
+# esp-idf-sys downloads the pinned ESP-IDF automatically. Set IDF_PATH in the
+# environment to reuse an existing installation (see README.md).
 set -euo pipefail
 
 cd "$(dirname "$0")/.."
 
+# Resolve the SDK defaults/components from this repository even when the build
+# cache is elsewhere, and copy the partition table into the CMake project.
+export CARGO_WORKSPACE_DIR="$PWD"
+export ESP_IDF_GLOB_BASE="$PWD"
+export ESP_IDF_GLOB_PARTITIONS="partitions.csv"
+
 if [ -f .env ]; then
     set -a
     # shellcheck disable=SC1091
@@ -19,4 +23,4 @@ fi
 : "${WIFI_SSID:?set WIFI_SSID in .env (or export it) before building}"
 export WIFI_PASS="${WIFI_PASS:-}"
 
-cargo build --release "$@"
+cargo build --release --locked "$@"