feat(auth): 비밀번호 표시 토글을 SVG 아이콘으로 통일

- AuthPasswordVisibilityToggle 공통 컴포넌트 추가
- signin·signup(비밀번호·확인)에 적용, 접근성 field-name 구분
- v0.0.61 문서 반영

Co-authored-by: Cursor <cursoragent@cursor.com>

pages/signin.vue

@@ -53,7 +53,7 @@ const submitSignIn = async () => {
 <template>
   <section class="auth-signin min-h-screen bg-[#0a0b0d] text-[#f5f7fa]">
     <div class="mx-auto flex min-h-screen w-full max-w-[1280px] items-center px-5 py-12 sm:px-10 lg:px-16">
-      <div class="w-full max-w-[430px] rounded-2xl border border-[#1a212a] bg-[#0d1116] p-5 sm:p-8">
+      <div class="w-full max-w-[430px] p-5 sm:p-8">
         <p class="text-2xl font-semibold leading-tight">
           로그인
         </p>
@@ -77,17 +77,11 @@ const submitSignIn = async () => {
             <div class="flex items-center rounded-[8px] border border-[#1a212a] transition-colors focus-within:border-[#2f6feb]">
               <input
                 v-model="form.password"
-                class="h-10 w-full bg-transparent px-3 text-sm outline-none"
+                class="h-10 min-w-0 flex-1 bg-transparent px-3 text-sm outline-none"
                 :type="showPassword ? 'text' : 'password'"
                 autocomplete="current-password"
               >
-              <button
-                class="px-3 text-xs text-[#9ba3af] transition-opacity hover:opacity-80"
-                type="button"
-                @click="showPassword = !showPassword"
-              >
-                {{ showPassword ? '숨기기' : '보기' }}
-              </button>
+              <AuthPasswordVisibilityToggle v-model="showPassword" />
             </div>
           </div>