feat(gui): Electron desktop with embedded core, tray, autostart, win/linux packaging

- cmd/gui: Electron shell (Clash-Verge style) embedding the full WebUI 1:1
  - embedded llmsproxy core (luajit) with auto-generated profile
  - key stored in keys[] (non-seed) so no replace-the-key warning
  - gw_key cookie injection: web UI works without login
  - side-rail toggles for autostart / silent start
  - system tray with status + controls, silent start (--silent)
  - win cross-build (mingw luajit exe + dll) / deb / AppImage via electron-builder
- Makefile: build / gui / gui-dist / gui-deb / gui-win targets
- README: desktop GUI section
- lua(adapter): opencode normalizes non-whitelisted roles to system

Makefile

@@ -0,0 +1,57 @@
+.PHONY: all build test gui gui-dev gui-dist gui-deb gui-win help clean
+
+# ModelRouter - single-binary gateway + optional Electron desktop GUI (embedded core)
+export BINARY
+BINARY=llmsproxy
+export BUILD_DIR
+BUILD_DIR=build
+export GUI_DIR
+GUI_DIR=cmd/gui
+VERSION ?= $(shell git describe --tags --dirty 2>/dev/null || echo "0.1.0")
+
+all: build
+
+# ---- core binary (server users / embedded core) ----
+build:
+	@mkdir -p $(BUILD_DIR)
+	CGO_ENABLED=1 go build -tags luajit -trimpath -o $(BUILD_DIR)/$(BINARY) ./cmd/llmsproxy
+	@echo "Built: $(BUILD_DIR)/$(BINARY) ($(VERSION))"
+
+# ---- GUI (Electron) ----
+gui:
+	@cd $(GUI_DIR) && npm start
+
+gui-dev:
+	@cd $(GUI_DIR) && npm run dev
+
+# build the embedded core into the GUI, then run electron-builder
+# targets: deb + AppImage (linux), rpm needs system rpmbuild
+gui-dist:
+	@cd $(GUI_DIR) && npm run dist:linux
+
+# deb only (for local sharing), rpm needs rpmbuild
+gui-deb:
+	@cd $(GUI_DIR) && npm run dist:debian
+
+# windows nsis installer (needs apt install gcc-mingw-w64-x86-64 + wine for electron-builder)
+gui-win:
+	@cd $(GUI_DIR) && npm run dist:win
+
+gui-dist-dir:
+	@cd $(GUI_DIR) && npm run dist:dir
+
+test:
+	go test ./...
+
+clean:
+	rm -rf $(BUILD_DIR) cmd/gui/build/gui-dist cmd/gui/bin
+
+help:
+	@echo "Targets:"
+	@echo "  make build      build core binary (luajit)"
+	@echo "  make gui        run desktop GUI (dev)"
+	@echo "  make gui-dev    run GUI with devtools"
+	@echo "  make gui-dist   build deb + AppImage (linux)"
+	@echo "  make gui-deb    build deb only"
+	@echo "  make gui-win    build Windows nsis (needs mingw + wine)"
+	@echo "  make test       run go tests"