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>

web/frontend/src/components/ui/index.ts

@@ -0,0 +1,19 @@
+export { default as Badge, badgeVariants } from './Badge.vue'
+export { default as Button, buttonVariants } from './Button.vue'
+export { default as Card } from './Card.vue'
+export { default as CardContent } from './CardContent.vue'
+export { default as CardDescription } from './CardDescription.vue'
+export { default as CardHeader } from './CardHeader.vue'
+export { default as CardTitle } from './CardTitle.vue'
+export { default as Input } from './Input.vue'
+export { default as Label } from './Label.vue'
+export { default as Modal } from './Modal.vue'
+export { default as Select } from './Select.vue'
+export { default as Separator } from './Separator.vue'
+export { default as Skeleton } from './Skeleton.vue'
+export { default as Switch } from './Switch.vue'
+export { default as Tabs } from './Tabs.vue'
+export { default as TabsContent } from './TabsContent.vue'
+export { default as TabsList } from './TabsList.vue'
+export { default as TabsTrigger } from './TabsTrigger.vue'
+export { default as Textarea } from './Textarea.vue'