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。

partitions.csv

@@ -1,17 +1,18 @@
 # Name,     Type, SubType,  Offset,   Size,     Flags
 #
-# The app partition offset here is chosen by scripts/flash.sh, not by hand. It
-# sits well above the usual 0x10000 because the module this firmware was first
-# brought up on has a defective byte in its SPI flash at 0xFADE7 (bits 5..7
+# The app partition offset must be validated against each rebuilt image. The
+# module this firmware was first brought up on has a defective byte in its SPI
+# flash at 0xFADE7 (bits 5..7
 # cannot be programmed). The app image is unchanged by where it is placed, so
 # moving the partition moves which image byte lands on that address - and
-# because a rebuild can shift the image again, re-deriving the offset by hand
+# because a rebuild can shift the image again, keeping an unchecked offset
 # would break on the next build. flash.sh picks the lowest 64 KB-aligned offset
 # whose byte at that address the flash can actually store, writes it back here,
 # and rebuilds.
 #
 # If you move to healthy hardware, put `factory` back at 0x10000 and delete
 # BAD_FLASH_ADDR from scripts/flash.sh; nothing else depends on this.
+# The same module also showed bit 6 read back high at 0x10863; keep factory >=0x20000.
 nvs,        data, nvs,      0x9000,   0x6000,
 phy_init,   data, phy,      0xf000,   0x1000,
-factory,    app,  factory,  0x060000,  0x120000,
+factory,    app,  factory,  0x070000,  0x120000,