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>

Makefile

@@ -0,0 +1,46 @@
+GO ?= go
+NPM ?= npm
+
+VERSION ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
+COMMIT ?= $(shell git rev-parse --short HEAD 2>/dev/null)
+LDFLAGS := -s -w \
+	-X github.com/apernet/OpenGFW/cmd.appVersion=$(VERSION) \
+	-X github.com/apernet/OpenGFW/cmd.appCommit=$(COMMIT)
+
+FRONTEND := web/frontend
+
+.PHONY: all
+all: web build
+
+## build: build the OpenGFW binary (embeds the web UI in web/dist)
+.PHONY: build
+build:
+	$(GO) build -o OpenGFW -ldflags "$(LDFLAGS)" .
+
+## web: build the web UI into web/dist
+.PHONY: web
+web:
+	cd $(FRONTEND) && $(NPM) install && $(NPM) run build
+
+## web-dev: run the Vite dev server against a local OpenGFW instance
+.PHONY: web-dev
+web-dev:
+	cd $(FRONTEND) && $(NPM) run dev
+
+## devserver: serve the web UI with synthetic data (works on any OS)
+.PHONY: devserver
+devserver:
+	$(GO) run ./web/devserver
+
+.PHONY: test
+test:
+	$(GO) test ./...
+
+.PHONY: vet
+vet:
+	$(GO) vet ./...
+
+.PHONY: clean
+clean:
+	rm -f OpenGFW
+	rm -rf $(FRONTEND)/node_modules