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/serial_soak.py

@@ -0,0 +1,124 @@
+#!/usr/bin/env python3
+"""Record firmware telemetry continuously (requires pyserial; no UDP subscriber)."""
+import argparse
+from datetime import datetime, timezone
+import json
+import math
+from pathlib import Path
+import re
+import sys
+import time
+
+import serial
+
+
+FIELDS = {
+    'submitted_fps': (r'([\d.]+) fps submitted', float),
+    'attempted_fps': (r'([\d.]+) fps attempted', float),
+    'kilobytes_per_second': (r'([\d.]+) kB/s', float),
+    'send_failures': (r'(\d+) send failures', int),
+    'retries': (r'(\d+) retries', int),
+    'peer_frames_dropped': (r'(\d+) peer frames dropped', int),
+    'send_ms': (r'([\d.]+) ms/send', float),
+    'subscribers': (r'(\d+) clients subscribed', int),
+    'heap_free': (r'internal heap (\d+) free', int),
+    'heap_largest': (r'free / (\d+) largest bytes', int),
+    'rssi_dbm': (r'RSSI (-?\d+) dBm', int),
+    'max_tx_power_dbm': (r'max TX power ([\w.+-]+) dBm', float),
+    'chip_temperature_c': (r'chip temp ([\w.+-]+) C', float),
+    'target_fps': (r'target (\d+) fps', int),
+    'capture_errors': (r'capture errors (\d+)', int),
+    'exposure_lines': (r'exposure (-?\d+) lines', int),
+    'jpeg_quality': (r'jpeg quality (\d+)', int),
+    'gain_multiplier': (r'gain ([\d.]+)x', float),
+    'capture_queue_skipped': (r'capture queue skipped (\d+)', int),
+    'stale_frames_dropped': (r'stale frames dropped (\d+)', int),
+    'deadline_peer_drops': (r'deadline peer drops (\d+)', int),
+    'max_submitted_capture_age_ms': (r'max submitted capture age ([\d.]+) ms', float),
+    'max_send_hold_ms': (r'max send hold ([\d.]+) ms', float),
+}
+
+
+def parse_sample(line):
+    if 'fps submitted' not in line:
+        return None
+    sample = {}
+    match = re.search(r'\((\d+)\)', line)
+    if match:
+        sample['uptime_ms'] = int(match[1])
+    for name, (pattern, convert) in FIELDS.items():
+        match = re.search(pattern, line)
+        if match:
+            value = convert(match[1])
+            sample[name] = value if not isinstance(value, float) or math.isfinite(value) else None
+    sample['thermal_limited'] = 'thermal_limited true' in line
+    return sample
+
+
+def write_json(path, data):
+    temporary = path.with_suffix(path.suffix+'.tmp')
+    temporary.write_text(json.dumps(data, ensure_ascii=False, indent=2)+'\n', encoding='utf-8')
+    temporary.replace(path)
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('--port', default='COM7')
+    parser.add_argument('--seconds', type=float, default=1860)
+    parser.add_argument('--out', type=Path, required=True, help='Output path prefix')
+    parser.add_argument('--reset', action='store_true')
+    parser.add_argument('--stop-file', type=Path, help='Finish cleanly when this file exists')
+    args = parser.parse_args()
+    args.out.parent.mkdir(parents=True, exist_ok=True)
+    port = serial.Serial()
+    port.port, port.baudrate, port.timeout = args.port, 115200, .2
+    port.dtr = port.rts = False
+    records, events = [], []
+    started = time.perf_counter()
+    last_uptime, reboot_count, last_sample_at = None, 0, None
+    serial_error = None
+    try:
+        port.open()
+        if args.reset:
+            port.rts = True
+            time.sleep(.15)
+            port.rts = False
+        with args.out.with_suffix('.serial.log').open('w', encoding='utf-8') as raw, args.out.with_suffix('.telemetry.ndjson').open('w', encoding='utf-8') as telemetry:
+            while time.perf_counter()-started < args.seconds:
+                if args.stop_file and args.stop_file.exists():
+                    break
+                line = port.readline().decode('utf-8', errors='replace')
+                if not line:
+                    continue
+                raw.write(line)
+                raw.flush()
+                elapsed = time.perf_counter()-started
+                sample = parse_sample(line)
+                if sample:
+                    sample.update(elapsed_seconds=round(elapsed, 3), utc=datetime.now(timezone.utc).isoformat())
+                    uptime = sample.get('uptime_ms')
+                    if uptime is not None and last_uptime is not None and uptime+1000 < last_uptime:
+                        reboot_count += 1
+                    last_uptime = uptime
+                    last_sample_at = elapsed
+                    records.append(sample)
+                    telemetry.write(json.dumps(sample)+'\n')
+                    telemetry.flush()
+                    write_json(args.out.with_suffix('.latest.json'), dict(elapsed_seconds=round(elapsed, 3), samples=len(records), reboot_count=reboot_count, latest=sample))
+                    if len(records) % 12 == 0:
+                        print(json.dumps(dict(minutes=round(elapsed/60, 1), reboot_count=reboot_count, latest=sample)), flush=True)
+                elif re.search(r'panic|Guru Meditation|Brownout|watchdog|NO-EOI|OVF|thermal load limit|reset reason|capture cap|configured capture', line, re.I):
+                    events.append(dict(elapsed_seconds=round(elapsed, 3), text=line.strip()))
+    except (serial.SerialException, OSError) as error:
+        serial_error = str(error)
+    finally:
+        port.close()
+        result = dict(elapsed_seconds=round(time.perf_counter()-started, 3), requested_seconds=args.seconds, stopped_by_request=bool(args.stop_file and args.stop_file.exists()), serial_error=serial_error, samples=len(records), reboot_count=reboot_count, last_sample_at=last_sample_at, events=events, records=records)
+        write_json(args.out.with_suffix('.summary.json'), result)
+    print(json.dumps({k:v for k,v in result.items() if k not in ('records', 'events')}))
+    if serial_error:
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main()