feat: add embedded web UI

Adds an optional web dashboard served by OpenGFW itself, enabled with a new
`web` section in the config file.

Backend (web package, decoupled from engine/io so it builds on any OS):
- hub.go collects statistics off the engine logger callbacks: atomic counters,
  two ring-buffered time series (10s and 1min buckets), top N hosts/blocked
  destinations/rules/analyzers, and a 512 entry event buffer fanned out to
  connected clients over SSE. Slow clients drop frames instead of blocking
  the engine.
- api.go exposes /api/v1 for info, meta, metrics, events, the SSE stream and
  ruleset read/validate/replace.
- auth.go implements password login with in-memory session tokens and login
  rate limiting. Mutating endpoints require the bearer token (the session
  cookie is only accepted for GET), which makes them CSRF-safe.
- cmd/web.go implements the rule manager: rules are compiled before anything
  is written, the file is replaced atomically and the engine is hot reloaded.
  The SIGHUP handler now shares that same path.
- web/devserver serves the UI with synthetic traffic for frontend work on
  machines where the engine itself cannot be built.

Frontend (web/frontend, Vue 3 + Vite + Tailwind CSS v4 + Reka UI):
dashboard, live event feed with analyzer property inspection, visual and YAML
rule editors, analyzer overview and settings. Responsive down to phone sizes
with a bottom tab bar and bottom-sheet dialogs, plus light/dark themes and
English/Chinese translations.

The built UI in web/dist is committed and embedded with go:embed so that
`go build` works without Node; CI builds the frontend and checks that the
committed output is up to date.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.zh.md

@@ -29,7 +29,26 @@ Telegram 群组： https://t.me/OpGFW
 - 规则可以热重载 (发送 `SIGHUP` 信号)
 - 灵活的协议解析和修改框架
 - 可扩展的 IO 实现 (目前只有 NFQueue)
-- [开发中] Web UI
+- Web UI，包含实时流量面板与规则编辑器
+
+## Web UI
+
+OpenGFW 内置了一个可选的 Web 控制面板：实时流量统计、带解析器属性的实时事件流，以及可以校验并热加载规则的规则编辑器。
+界面同时适配手机和桌面浏览器。
+
+在配置文件中启用：
+
+```yaml
+web:
+  enabled: true
+  listen: :8080
+  secret: 你的密码 # 留空则启动时随机生成并打印到日志
+  # cert: /path/to/fullchain.pem
+  # key: /path/to/privkey.pem
+```
+
+前端已经打包进二进制文件，无需额外部署静态资源。请只在可信网络中开放该端口——拿到密码即可修改你的规则。
+开发说明见 [web/README.md](web/README.md)。
 
 ## 使用场景