refactor(routes):

- keep install-mode root redirect to /install and add tests covering install root redirect and install page serving
- change root backend handler from Any("/") to POST("/") so GET / can consistently serve the SPA after install

Co-authored-by: Copilot <copilot@github.com>

src/route/router.go

@@ -22,7 +22,7 @@ import (
 
 // RegisterRoute 路由注册
 func RegisterRoute(e *echo.Echo) {
-	e.Any("/", func(c echo.Context) error {
+	e.POST("/", func(c echo.Context) error {
 		return c.String(http.StatusOK, "hello epusdt, https://github.com/GMwalletApp/epusdt")
 	})