feat(extension): browser extension for Chrome/Edge/Firefox + CI + v0.8.0

Adds a WXT-based browser extension that replaces manual JS snippet
injection for AI-driven browser testing. The extension auto-connects
to the Muyue server via WebSocket on every page, using the exact
same protocol as the existing snippet — zero backend changes needed.

- Chrome/Edge (MV3) + Firefox (MV2) from single codebase via WXT
- Content script: auto-connect WS, console capture, URL tracking, RPC
- Background service worker: token management, screenshots, badge
- Popup + side panel with server status, sessions, URL config
- CI workflows: build extension, attach .zip to releases
- Makefile targets: ext, ext-chrome, ext-firefox, ext-zip
- Version bumped to 0.8.0

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

Makefile

@@ -7,7 +7,9 @@ NODE ?= node
 NPM ?= npm
 WEB_DIR = web
 
-.PHONY: build install clean test test-short run scan fmt lint build-all deps vet frontend dev-desktop
+EXT_DIR = extension
+
+.PHONY: build install clean test test-short run scan fmt lint build-all deps vet frontend dev-desktop ext ext-chrome ext-firefox ext-zip
 
 frontend:
 	cd $(WEB_DIR) && $(NPM) ci && $(NPM) run build
@@ -63,5 +65,17 @@ build-all: frontend
 	GOOS=windows GOARCH=amd64 $(GO) build -o dist/$(BINARY)-windows-amd64.exe ./cmd/muyue/
 	GOOS=windows GOARCH=arm64 $(GO) build -o dist/$(BINARY)-windows-arm64.exe ./cmd/muyue/
 
+ext:
+	cd $(EXT_DIR) && $(NPM) ci && $(NPM) run build && $(NPM) run build:firefox
+
+ext-chrome:
+	cd $(EXT_DIR) && $(NPM) ci && $(NPM) run build
+
+ext-firefox:
+	cd $(EXT_DIR) && $(NPM) ci && $(NPM) run build:firefox
+
+ext-zip:
+	cd $(EXT_DIR) && $(NPM) ci && $(NPM) run zip && $(NPM) run zip:firefox
+
 deps:
 	$(GO) mod tidy