CrossRelay stage 0+1: Go gateway with Anthropic<->Chat Completions relay, Tauri shell, bilingual management UI

- Go gateway (stdlib only): /v1/messages non-stream + SSE, /v1/messages/count_tokens,
  management API /api/* (providers CRUD, apply/restore, settings, backups, logs)
- Protocol conversion: Anthropic Messages <-> Chat Completions with a streaming
  state machine keyed by content block index (text, tool_use, parallel calls)
- ~/.claude/settings.json guarded read/write: timestamped backups, managed env
  keys only, one-click restore
- Tauri 2 shell: spawns the gateway sidecar, parses the random port from stdout,
  stdin pipe watchdog prevents orphans, kills the child on exit
- React frontend: Dashboard/Providers/Settings, zh-CN + en-US, TanStack Query
- Tests: Go table-driven + httptest integration (all green), vitest + RTL

Makefile

@@ -0,0 +1,29 @@
+ifeq ($(OS),Windows_NT)
+GATEWAY_BIN := bin/gateway.exe
+else
+GATEWAY_BIN := bin/gateway
+endif
+
+.PHONY: all build test fmt vet dev dev-gateway clean
+
+all: build
+
+build: $(GATEWAY_BIN)
+
+$(GATEWAY_BIN):
+	go build -o $(GATEWAY_BIN) ./cmd/gateway
+
+test:
+	go test ./...
+
+fmt:
+	go fmt ./...
+
+vet:
+	go vet ./...
+
+dev: build
+	npm run tauri dev
+
+clean:
+	rm -rf bin