fix: 自定义标签融入原生标签栏，点击切换而非消失

- StyleSelector 新增 customTags 属性，自定义标签作为「自定义标签」行展示在原生标签栏中
- 自定义标签点击切换 true/false，不再移除 key，解决点击消失问题
- CustomTagsEditor 简化为仅输入框+添加按钮
- extractTags 仅提取激活态自定义标签（value=true）
- 导出 CUSTOM_PREFIX 供组件使用

frontend/src/components/StyleSelector.tsx

@@ -1,5 +1,5 @@
 import type { StyleCategory } from '../utils/style'
-import { STYLE_CATEGORIES } from '../utils/style'
+import { STYLE_CATEGORIES, CUSTOM_PREFIX } from '../utils/style'
 import styles from './StyleSelector.module.css'
 
 interface StyleSelectorProps {
@@ -7,6 +7,13 @@ interface StyleSelectorProps {
   onChange: (key: string, value: string) => void
   compact?: boolean
   categories?: StyleCategory[]
+  customTags?: string[]
+}
+
+const CUSTOM_TAG_CATEGORY: StyleCategory = {
+  key: '', // unused, pills use custom: prefix directly
+  label: '自定义标签',
+  options: [],
 }
 
 export default function StyleSelector({
@@ -14,6 +21,7 @@ export default function StyleSelector({
   onChange,
   compact,
   categories,
+  customTags,
 }: StyleSelectorProps) {
   const cats = categories ?? STYLE_CATEGORIES
   return (
@@ -37,6 +45,27 @@ export default function StyleSelector({
           </div>
         </div>
       ))}
+      {customTags && customTags.length > 0 && (
+        <div key="_custom" className={styles.category}>
+          <span className={styles.label}>{CUSTOM_TAG_CATEGORY.label}</span>
+          <div className={styles.options}>
+            {customTags.map(tag => {
+              const key = `${CUSTOM_PREFIX}${tag}`
+              const isActive = value[key] === 'true'
+              return (
+                <button
+                  key={tag}
+                  type="button"
+                  className={`${styles.pill} ${isActive ? styles.pillActive : ''}`}
+                  onClick={() => onChange(key, isActive ? 'false' : 'true')}
+                >
+                  {tag}
+                </button>
+              )
+            })}
+          </div>
+        </div>
+      )}
     </div>
   )
 }