feat: 비밀번호 변경 UI (헤더 잠금 아이콘 + 모달)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/stores/ui.js

@@ -16,6 +16,15 @@ export const useUiStore = defineStore('ui', () => {
     sidebarOpen.value = false
   }
 
+  // 비밀번호 변경 모달
+  const passwordOpen = ref(false)
+  function openPassword() {
+    passwordOpen.value = true
+  }
+  function closePassword() {
+    passwordOpen.value = false
+  }
+
   // 로그인 팝업 (회원가입 팝업은 닫고 전환)
   function openLogin(redirect = '') {
     redirectPath.value = redirect || ''
@@ -39,5 +48,6 @@ export const useUiStore = defineStore('ui', () => {
   return {
     loginOpen, signupOpen, redirectPath, openLogin, closeLogin, openSignup, closeSignup,
     sidebarOpen, toggleSidebar, closeSidebar,
+    passwordOpen, openPassword, closePassword,
   }
 })