refactor: migrate img tags to next/image and fix hook usage

src/app/auth/components/auth-email-panel.tsx

@@ -13,6 +13,7 @@
  *   - Spacer + AuthLegalText
  *   - 顶部 "← Back" 按钮由父级 AuthPanel 渲染（悬浮 40×40 圆形）
  */
+import Image from "next/image";
 import { useState } from "react";
 
 import { useAuthState } from "@/stores/auth/auth-context";
@@ -48,10 +49,13 @@ export function AuthEmailPanel({
         {mode === "login" ? (
           <>
             <div className={styles.spacer24} />
-            <img
+            <Image
               src="/images/auth/ic-logo-login.png"
               alt="Cozsweet"
+              width={120}
+              height={120}
               className={styles.logo}
+              priority
             />
           </>
         ) : (

src/app/auth/components/auth-facebook-panel.tsx

@@ -11,6 +11,7 @@
  *   - "Other Sign-in Options" 链接打开底部弹层
  *   - 弹层 Email 按钮 → 触发 `onSwitchToEmail`（父级派发 `AuthPanelModeChanged`）
  */
+import Image from "next/image";
 import { useState } from "react";
 
 import { AuthPlatform } from "@/lib/auth/nextauth";
@@ -56,10 +57,13 @@ export function AuthFacebookPanel({ onSwitchToEmail }: AuthFacebookPanelProps) {
   return (
     <div className={styles.panel}>
       <div className={styles.spacer} />
-      <img
+      <Image
         src="/images/auth/ic-logo-login.png"
         alt="Cozsweet"
+        width={120}
+        height={120}
         className={styles.logo}
+        priority
       />
       <div className={styles.spacer} />