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/scripts/test-stream.mjs

@@ -0,0 +1,143 @@
+import { readFileSync } from 'node:fs';
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+import ts from 'typescript';
+
+const source = readFileSync(new URL('../src/lib/stream.ts', import.meta.url), 'utf8');
+const compiled = ts.transpileModule(source, { compilerOptions: { module: ts.ModuleKind.CommonJS, target: ts.ScriptTarget.ES2022 } }).outputText;
+const exports = {};
+new Function('require', 'exports', compiled)(name => {
+  assert.equal(name, './types');
+  return { FRAME_HEADER_LEN: 16 };
+}, exports);
+const { StreamClient } = exports;
+globalThis.window = { clearTimeout, setTimeout };
+const tick = () => new Promise(resolve => setImmediate(resolve));
+const bitmap = () => ({ closed: false, close() { this.closed = true; } });
+function frame(id, camera = 42) {
+  const bytes = new ArrayBuffer(20);
+  const header = new DataView(bytes);
+  header.setUint32(0, camera, true);
+  header.setUint32(4, id, true);
+  header.setUint16(8, 640, true);
+  header.setUint16(10, 480, true);
+  header.setUint32(12, 4, true);
+  return bytes;
+}
+function client(now, wallNow) { return new StreamClient({ onMessage() {}, onConnection() {} },now,wallNow); }
+function deferredDecoder() {
+  const requests = [];
+  globalThis.createImageBitmap = () => new Promise((resolve, reject) => requests.push({ resolve, reject }));
+  return requests;
+}
+
+test('a slow decoder keeps only the latest pending frame for each camera', async () => {
+  const requests = deferredDecoder();
+  const rx = client();
+  const finished = rx.onBinary(frame(1));
+  for (let id = 2; id <= 100; id++) await rx.onBinary(frame(id));
+  assert.equal(requests.length, 1);
+  assert.equal(rx.pending.size, 1);
+  const first = bitmap();
+  requests[0].resolve(first);
+  await tick();
+  assert.equal(requests.length, 2);
+  requests[1].resolve(bitmap());
+  await finished;
+  assert.equal(rx.latest(42).frameId, 100);
+  assert.equal(rx.counters.skippedDecodes, 98);
+  assert.equal(first.closed, true);
+  rx.close();
+});
+
+test('two cameras decode independently without queues growing behind either', async () => {
+  const requests = deferredDecoder();
+  const rx = client();
+  const a = rx.onBinary(frame(1, 1));
+  const b = rx.onBinary(frame(2, 2));
+  assert.equal(requests.length, 2);
+  requests[1].resolve(bitmap());
+  await b;
+  assert.equal(rx.latest(2).frameId, 2);
+  assert.equal(rx.latest(1), undefined);
+  requests[0].resolve(bitmap());
+  await a;
+  rx.close();
+});
+
+test('closing during decode releases the late bitmap and discards pending work', async () => {
+  const requests = deferredDecoder();
+  const rx = client();
+  const work = rx.onBinary(frame(1));
+  await rx.onBinary(frame(2));
+  rx.close();
+  const late = bitmap();
+  requests[0].resolve(late);
+  await work;
+  assert.equal(late.closed, true);
+  assert.equal(requests.length, 1);
+  assert.equal(rx.latest(42), undefined);
+});
+
+test('a corrupt JPEG does not stop the next frame from being decoded', async () => {
+  const requests = deferredDecoder();
+  const rx = client();
+  const work = rx.onBinary(frame(1));
+  await rx.onBinary(frame(2));
+  requests[0].reject(new Error('bad JPEG'));
+  await tick();
+  requests[1].resolve(bitmap());
+  await work;
+  assert.equal(rx.counters.decodeFailures, 1);
+  assert.equal(rx.latest(42).frameId, 2);
+  rx.close();
+});
+
+test('late frames are rejected but a reboot after silence can restart the counter', () => {
+  const rx = client();
+  rx.injectFrame(42, 100, 640, 480, bitmap());
+  const old = bitmap();
+  rx.injectFrame(42, 99, 640, 480, old);
+  assert.equal(old.closed, true);
+  assert.equal(rx.latest(42).frameId, 100);
+  rx.latest(42).receivedAt -= 2000;
+  rx.injectFrame(42, 1, 640, 480, bitmap());
+  assert.equal(rx.latest(42).frameId, 1);
+  rx.close();
+});
+
+test('a WebView backlog is discarded before JPEG decoding using native host timing', async () => {
+  const requests = deferredDecoder();
+  const rx = client(() => 0, () => 2000);
+  rx.onTiming({camera:42,frameId:1,publishedUnixMs:1500});
+  await rx.onBinary(frame(1));
+  assert.equal(requests.length,0);
+  assert.equal(rx.counters.staleFrames,1);
+  rx.onTiming({camera:42,frameId:2,publishedUnixMs:2000});
+  const work = rx.onBinary(frame(2));
+  requests[0].resolve(bitmap());await work;
+  assert.equal(rx.latest(42).frameId,2);
+  rx.close();
+});
+
+test('a blocked decoder releases its old result and resumes with the fresh pending frame', async () => {
+  let clock=0;
+  const requests=deferredDecoder(),rx=client(()=>clock);
+  const work=rx.onBinary(frame(1));
+  clock=110;await rx.onBinary(frame(2));
+  const old=bitmap();requests[0].resolve(old);await tick();
+  assert.equal(old.closed,true);
+  assert.equal(rx.latest(42),undefined);
+  requests[1].resolve(bitmap());await work;
+  assert.equal(rx.latest(42).frameId,2);
+  assert.equal(rx.counters.staleFrames,1);rx.close();
+});
+
+test('pending frames that expired during a decoder stall never reach the decoder', async () => {
+  let clock=0;
+  const requests=deferredDecoder(),rx=client(()=>clock);
+  const work=rx.onBinary(frame(1));await rx.onBinary(frame(2));
+  clock=200;const old=bitmap();requests[0].resolve(old);await work;
+  assert.equal(old.closed,true);assert.equal(requests.length,1);
+  assert.equal(rx.counters.staleFrames,2);assert.equal(rx.latest(42),undefined);rx.close();
+});