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。

components/cam_wrapper/include/cam_wrapper.h

@@ -112,6 +112,8 @@ typedef struct {
     size_t height;
     int format;
     void *handle; /* internal driver frame; do not touch */
+    int64_t capture_started_us; /* same monotonic clock as esp_timer_get_time */
+    uint32_t skipped_before; /* older completed frames released by latest get */
 } cam_wrapper_fb_t;
 
 esp_err_t cam_wrapper_init(const cam_wrapper_config_t *config, cam_wrapper_sensor_t sensor);
@@ -119,6 +121,7 @@ esp_err_t cam_wrapper_init(const cam_wrapper_config_t *config, cam_wrapper_senso
 /* Acquire one frame into `out`. Returns ESP_OK on success, ESP_FAIL if the
  * driver could not hand out a frame (e.g. timeout or buffer starvation). */
 esp_err_t cam_wrapper_fb_get(cam_wrapper_fb_t *out, cam_wrapper_sensor_t sensor);
+esp_err_t cam_wrapper_fb_get_latest(cam_wrapper_fb_t *out, uint32_t timeout_ms);
 
 void cam_wrapper_fb_release(cam_wrapper_fb_t *fb);
 
@@ -129,6 +132,26 @@ esp_err_t cam_wrapper_deinit(void);
 /* Name of the sensor the driver detected, or "unknown". Never NULL. */
 const char *cam_wrapper_sensor_name(void);
 
+/* Keep the sensor's JPEG encoder; effect 2 removes chroma in the sensor ISP. */
+esp_err_t cam_wrapper_set_grayscale(int enabled);
+/* Runtime JPEG compression, 0..63, without restarting the camera pipeline. */
+esp_err_t cam_wrapper_set_quality(unsigned quality);
+/* OV5640 target bias: 0 = default, -1 / -2 select approximately -1.1 / -1.9 EV. */
+esp_err_t cam_wrapper_set_exposure_bias(int ev);
+/* 0 = auto shutter; nonzero holds that exposure in sensor lines, AGC stays on. */
+esp_err_t cam_wrapper_set_shutter_lines(unsigned lines);
+/* Keep AEC/AGC automatic, cap exposure lines, and disable night frame extension. */
+esp_err_t cam_wrapper_set_exposure_limit(unsigned lines);
+/* 0 keeps the driver timing; nonzero changes OV5640 horizontal total only. */
+esp_err_t cam_wrapper_set_horizontal_timing(unsigned hts);
+int cam_wrapper_exposure_lines(void);
+/* OV5640 gain in 1/16 units; -1 when unavailable. */
+int cam_wrapper_gain_raw(void);
+float cam_wrapper_probe_frame_rate(void);
+/* Silicon temperature, not ambient or camera-sensor temperature. */
+esp_err_t cam_wrapper_temperature_init(void);
+esp_err_t cam_wrapper_temperature_read(float *celsius);
+
 #ifdef __cplusplus
 }
-#endif
+#endif