refactor: restructure project to standard Go layout

- Reorganize code into cmd/bilidown and internal/ packages
- Rename client/ to web/ for frontend source
- Remove systray dependency for headless web service
- Embed static files into binary using go:embed
- Update import paths to use internal/ prefix
- Update .gitignore with common patterns

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/index.ts

@@ -0,0 +1,28 @@
+/// <reference types="vite/client" />
+import van from 'vanjs-core'
+import Header from './header'
+import Work from './work'
+import Task from './task'
+import Login from './login'
+import Setting from './setting'
+import _Error from './error'
+import { redirect } from 'vanjs-router'
+import { GLOBAL_HIDE_PAGE } from './mixin'
+import 'bootstrap/dist/css/bootstrap.min.css'
+import './scss/index.scss'
+import { PlayerModalComp } from './task/playerModal'
+
+const { div } = van.tags
+
+redirect('home', 'work')
+
+van.add(document.body,
+    div({ class: 'container py-4 vstack gap-4', hidden: GLOBAL_HIDE_PAGE },
+        Header(),
+        Work(),
+        Task(),
+        Login(),
+        Setting(),
+    ),
+    _Error()
+)