feat(css): 优化主题切换图标显示逻辑

- 调整图标显示规则，确保日夜模式下图标正确隐藏
- 移除重复的图标隐藏样式定义
- 删除已弃用的MBTI标签渐变色样式
- 保持样式代码结构清晰一致

css/about.css

@@ -147,6 +147,14 @@ body {
     text-shadow: 0 0 10px var(--accent);
 }
 
+[data-theme="day"] .icon-sun {
+    display: none;
+}
+
+[data-theme="night"] .icon-moon {
+    display: none;
+}
+
 
 /* =========================================
    3. Navigation
@@ -250,14 +258,6 @@ body {
     .action-btn:active {
         transform: translateY(0);
     }
-
-    [data-theme="day"] .icon-sun {
-        display: none;
-    }
-
-    [data-theme="night"] .icon-moon {
-        display: none;
-    }
 }
 
 /* =========================================
@@ -646,33 +646,6 @@ body {
     max-width: 100%;
 }
 
-.mbti-tags .tag.tag-color-1 {
-    background: var(--gradient-1);
-    -webkit-background-clip: text;
-    background-clip: text;
-    color: transparent;
-}
-
-.mbti-tags .tag.tag-color-2 {
-    background: var(--gradient-2);
-    -webkit-background-clip: text;
-    background-clip: text;
-    color: transparent;
-}
-
-.mbti-tags .tag.tag-color-3 {
-    background: var(--gradient-3);
-    -webkit-background-clip: text;
-    background-clip: text;
-    color: transparent;
-}
-
-.mbti-tags .tag.tag-color-4 {
-    background: var(--gradient-4);
-    -webkit-background-clip: text;
-    background-clip: text;
-    color: transparent;
-}
 
 /* --- Tech Stack (PC) --- */
 .area-tech {
@@ -1479,14 +1452,6 @@ body {
     .action-btn:active {
         transform: translateY(0);
     }
-
-    [data-theme="day"] .icon-sun {
-        display: none;
-    }
-
-    [data-theme="night"] .icon-moon {
-        display: none;
-    }
 }
 
 /* =========================================

js/about.js

@@ -182,7 +182,7 @@ class ThemeManager {
 
     init() {
         let theme = getStoredTheme();
-        if (theme === 'night') this.root.setAttribute('data-theme', 'night');
+        if (theme) this.root.setAttribute('data-theme', theme);
         $('#theme-btn').toggleClass('is-active', theme === 'night');
         const langForTitle = getStoredLanguage();
         const titleText = theme === 'night' ? (langForTitle === 'zh' ? '白天模式' : 'Day') : (langForTitle === 'zh' ? '黑夜模式' : 'Night');
@@ -191,7 +191,7 @@ class ThemeManager {
         $('#theme-btn').on('click', () => {
             const curr = this.root.getAttribute('data-theme');
             const next = curr === 'night' ? 'day' : 'night';
-            if (next === 'night') this.root.setAttribute('data-theme', 'night');
+            if (next) this.root.setAttribute('data-theme', next);
             else this.root.removeAttribute('data-theme');
             setStoredTheme(next)
             $('#theme-btn').toggleClass('is-active', next === 'night');