外观设置改为单页分区；发帖草稿与板块校验优化，WS 延迟释放避开 Strict Mode 误断。

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

frontend/components/BoardPicker.tsx

@@ -10,6 +10,8 @@ type BoardPickerProps = {
   onChange: (id: number) => void;
   disabled?: boolean;
   loading?: boolean;
+  /** 提交校验失败后再为 true，用于红色错误态 */
+  invalid?: boolean;
   id?: string;
 };
 
@@ -23,6 +25,7 @@ export default function BoardPicker({
   onChange,
   disabled,
   loading,
+  invalid = false,
   id,
 }: BoardPickerProps) {
   const listId = useId();
@@ -92,6 +95,7 @@ export default function BoardPicker({
   };
 
   const empty = !loading && !selected;
+  const showError = empty && invalid;
   const label = loading
     ? "加载板块…"
     : selected
@@ -109,12 +113,12 @@ export default function BoardPicker({
       <button
         id={id}
         type="button"
-        className={`j13-board-trigger${empty ? " is-empty" : ""}`}
+        className={`j13-board-trigger${showError ? " is-invalid" : ""}`}
         disabled={disabled || loading || boards.length === 0}
         aria-haspopup="listbox"
         aria-expanded={open}
         aria-controls={listId}
-        aria-invalid={empty || undefined}
+        aria-invalid={showError || undefined}
         onClick={() => setOpen((v) => !v)}
         onKeyDown={onTriggerKeyDown}
       >
@@ -126,7 +130,9 @@ export default function BoardPicker({
         </span>
         <span className="j13-board-trigger-copy">
           <span className="j13-board-trigger-name">{label}</span>
-          {empty ? (
+          {showError ? (
+            <span className="j13-board-trigger-hint">请选择板块后再发布</span>
+          ) : empty ? (
             <span className="j13-board-trigger-hint">发布前必须选择</span>
           ) : loading ? (
             <span className="j13-board-trigger-hint">正在加载</span>