fix(admin): 后台入口 /admin /login 用 sendRedirect 产生真实 302

@RestController 下返回 redirect: 字符串只会原样写进 200 响应体，
浏览器不会跳转。页面入口方法改为 HttpServletResponse.sendRedirect 302
到 /admin-vue/，旧 /admin.html、/login.html 一并兜底。

backend-java/src/main/java/com/nanri/aiimage/modules/admin/controller/AdminConsoleController.java

@@ -9,10 +9,12 @@ import com.nanri.aiimage.modules.permission.service.support.AdminMenuTreeBuilder
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
 import lombok.RequiredArgsConstructor;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+import java.io.IOException;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -37,26 +39,26 @@ public class AdminConsoleController {
 
     @GetMapping("/")
     @Operation(summary = "根路径跳管理后台", hidden = true)
-    public String root() {
-        return "redirect:/admin-vue/";
+    public void root(HttpServletResponse response) throws IOException {
+        response.sendRedirect("/admin-vue/");
     }
 
     @GetMapping({"/admin", "/admin.html"})
     @Operation(summary = "管理后台入口（含旧 /admin.html 兜底）", hidden = true)
-    public String adminPage() {
-        return "redirect:/admin-vue/";
+    public void adminPage(HttpServletResponse response) throws IOException {
+        response.sendRedirect("/admin-vue/");
     }
 
     @GetMapping({"/login", "/login.html"})
     @Operation(summary = "登录页入口（含旧 /login.html 兜底）", hidden = true)
-    public String loginPage() {
-        return "redirect:/admin-vue/login";
+    public void loginPage(HttpServletResponse response) throws IOException {
+        response.sendRedirect("/admin-vue/login");
     }
 
     @GetMapping("/logout")
     @Operation(summary = "登出 GET 兜底（POST 走 auth 模块）", hidden = true)
-    public String logoutPage() {
-        return "redirect:/admin-vue/login";
+    public void logoutPage(HttpServletResponse response) throws IOException {
+        response.sendRedirect("/admin-vue/login");
     }
 
     @GetMapping("/api/admin/current-user")