feat: PC 프로필에 POP 모드 전환 + PC전환 시 전체화면 해제

- PC UserDropdown에 "POP 모드" 메뉴 추가 (결재함↔로그아웃 사이)
- POP→PC 전환 시 전체화면 자동 해제

frontend/components/layout/UserDropdown.tsx

@@ -8,7 +8,7 @@ import {
   DropdownMenuSeparator,
   DropdownMenuTrigger,
 } from "@/components/ui/dropdown-menu";
-import { LogOut, User, FileCheck } from "lucide-react";
+import { LogOut, User, FileCheck, Smartphone } from "lucide-react";
 import { useRouter } from "next/navigation";
 
 interface UserDropdownProps {
@@ -86,6 +86,10 @@ export function UserDropdown({ user, onProfileClick, onLogout }: UserDropdownPro
           <FileCheck className="mr-2 h-4 w-4" />
           <span>결재함</span>
         </DropdownMenuItem>
+        <DropdownMenuItem onClick={() => router.push("/pop/home")}>
+          <Smartphone className="mr-2 h-4 w-4" />
+          <span>POP 모드</span>
+        </DropdownMenuItem>
         <DropdownMenuSeparator />
         <DropdownMenuItem onClick={onLogout}>
           <LogOut className="mr-2 h-4 w-4" />

frontend/components/pop/hardcoded/PopShell.tsx

@@ -62,8 +62,11 @@ export function PopShell({ children, showBanner = true, title, showBack = false,
     };
   }, [profileOpen]);
 
-  const handlePcMode = () => {
+  const handlePcMode = async () => {
     setProfileOpen(false);
+    if (document.fullscreenElement) {
+      try { await document.exitFullscreen(); } catch {}
+    }
     router.push("/");
   };