feat: 浏览器端 CH340/CH341 WebUSB 驱动 + navigator.serial 垫片

- ch340-webusb.js: WebUSB 上完整的 USB-Serial 栈
  · CH340/CH341 vendor 控制传输初始化（对齐 Linux ch341.c）
  · 波特率分频算法 calcCh34xBaud（1532620800 基准）
  · bulk IN 32 深读队列 + ReadableStream / 4096 分片写 + WritableStream
  · DTR/RTS（0xA4 取反写入）、拔插事件、诊断计数
  · 附带 CDC-ACM(CH343/CH9102/CH347)、CP210x、FTDI(含 modem 字节剥离)、PL2303(HXN/HX/01/T)
- ch340-serial-shim.js: 安卓上补出 navigator.serial，老代码零改动可用
- ch340-test.html: 连接/收发/HEX/DTR-RTS/回环自测 测试台
- docs/ch34x-registers.md: 寄存器与控制传输逆向说明
- test/driver.test.mjs: 15 项 mock 断言（node，无需硬件）

package.json

@@ -0,0 +1,27 @@
+{
+  "name": "ch340-webusb",
+  "version": "1.0.0",
+  "description": "Browser driver for CH340/CH341 (and CDC-ACM/CP210x/FTDI/PL2303) USB-serial chips over WebUSB — works on Android Chrome, plus a navigator.serial shim.",
+  "main": "ch340-webusb.js",
+  "files": [
+    "ch340-webusb.js",
+    "ch340-serial-shim.js",
+    "ch340-test.html",
+    "docs",
+    "README.md",
+    "LICENSE"
+  ],
+  "scripts": {
+    "test": "node test/driver.test.mjs"
+  },
+  "keywords": [
+    "webusb",
+    "ch340",
+    "ch341",
+    "serial",
+    "android",
+    "web-serial",
+    "usb-serial"
+  ],
+  "license": "MIT"
+}