feat: EH Downloader 用 Go + Wails v2 重写

原 Electron 版在这台 Windows 机器上无法启动（0x80000003 崩在 V8 初始化），
整个业务逻辑用 Go 重写，前端界面与协议结论完全保留。

- internal/eh: 协议核心，画廊页分页 -> /s/ -> hath 直链 -> 下载
- internal/core: 并发引擎 / 状态存储 / 目录模板 / 油猴桥口
- app.go: Wails 绑定层，替代 Electron IPC
- frontend/js/api.js: 适配层，renderer.js 一行未改
- 37 个测试，含 httptest 模拟 EH 的端到端链路验证

相比 Electron 版：90MB -> 12.4MB，180MB 内存 -> 27MB，构建 90s -> 2s。

顺带修掉原版代理探测的 bug（永远返回第一个端口，从不等连接结果）。

frontend/wailsjs/go/main/App.d.ts

@@ -0,0 +1,42 @@
+// Cynhyrchwyd y ffeil hon yn awtomatig. PEIDIWCH Â MODIWL
+// This file is automatically generated. DO NOT EDIT
+import {main} from '../models';
+import {core} from '../models';
+
+export function AddTasks(arg1:string):Promise<main.AddTasksResult>;
+
+export function ClearAll(arg1:boolean):Promise<Record<string, any>>;
+
+export function ClearFinished():Promise<Record<string, any>>;
+
+export function CountDone():Promise<number>;
+
+export function ExportFailed(arg1:string):Promise<string>;
+
+export function GetSettings():Promise<core.Settings>;
+
+export function ListTasks():Promise<Array<core.Task>>;
+
+export function OpenPath(arg1:string):Promise<void>;
+
+export function PickDir():Promise<string>;
+
+export function Placeholders():Promise<Array<string>>;
+
+export function PreviewDir(arg1:string):Promise<main.DirPreviewResult>;
+
+export function RemoveTask(arg1:string,arg2:string):Promise<Array<core.Task>>;
+
+export function RequeueFailed():Promise<Array<core.Task>>;
+
+export function SelectAll(arg1:Array<string>):Promise<Array<core.Task>>;
+
+export function SetSettings(arg1:Record<string, any>):Promise<core.Settings>;
+
+export function ShowItem(arg1:string):Promise<void>;
+
+export function Start(arg1:Array<string>):Promise<main.StartResult>;
+
+export function Status():Promise<main.StatusResult>;
+
+export function Stop():Promise<Record<string, any>>;

frontend/wailsjs/go/main/App.js

@@ -0,0 +1,79 @@
+// @ts-check
+// Cynhyrchwyd y ffeil hon yn awtomatig. PEIDIWCH Â MODIWL
+// This file is automatically generated. DO NOT EDIT
+
+export function AddTasks(arg1) {
+  return window['go']['main']['App']['AddTasks'](arg1);
+}
+
+export function ClearAll(arg1) {
+  return window['go']['main']['App']['ClearAll'](arg1);
+}
+
+export function ClearFinished() {
+  return window['go']['main']['App']['ClearFinished']();
+}
+
+export function CountDone() {
+  return window['go']['main']['App']['CountDone']();
+}
+
+export function ExportFailed(arg1) {
+  return window['go']['main']['App']['ExportFailed'](arg1);
+}
+
+export function GetSettings() {
+  return window['go']['main']['App']['GetSettings']();
+}
+
+export function ListTasks() {
+  return window['go']['main']['App']['ListTasks']();
+}
+
+export function OpenPath(arg1) {
+  return window['go']['main']['App']['OpenPath'](arg1);
+}
+
+export function PickDir() {
+  return window['go']['main']['App']['PickDir']();
+}
+
+export function Placeholders() {
+  return window['go']['main']['App']['Placeholders']();
+}
+
+export function PreviewDir(arg1) {
+  return window['go']['main']['App']['PreviewDir'](arg1);
+}
+
+export function RemoveTask(arg1, arg2) {
+  return window['go']['main']['App']['RemoveTask'](arg1, arg2);
+}
+
+export function RequeueFailed() {
+  return window['go']['main']['App']['RequeueFailed']();
+}
+
+export function SelectAll(arg1) {
+  return window['go']['main']['App']['SelectAll'](arg1);
+}
+
+export function SetSettings(arg1) {
+  return window['go']['main']['App']['SetSettings'](arg1);
+}
+
+export function ShowItem(arg1) {
+  return window['go']['main']['App']['ShowItem'](arg1);
+}
+
+export function Start(arg1) {
+  return window['go']['main']['App']['Start'](arg1);
+}
+
+export function Status() {
+  return window['go']['main']['App']['Status']();
+}
+
+export function Stop() {
+  return window['go']['main']['App']['Stop']();
+}