feat(frontend): add posting compose component suite

新增了发帖相关的完整组件模块：包括顶部导航栏ComposeHeader、正文编辑区ComposeDocument，以及发布设置栏ComposeContextBar，同时添加了vite依赖缓存配置文件。

frontend/src/components/compose/ComposeContextBar.tsx

@@ -0,0 +1,105 @@
+import TagInput from '../TagInput';
+import BoardIconDisplay from '../BoardIconDisplay';
+import { getBoardThemeIndex } from '../../utils/boardTheme';
+import type { Board, ForumLimitsPublic } from '../../api/types';
+
+export type PostType = 'normal' | 'question';
+
+interface Props {
+  isEdit: boolean;
+  postType: PostType;
+  onPostTypeChange: (type: PostType) => void;
+  boards: Board[];
+  boardId: string;
+  onBoardChange: (boardId: string) => void;
+  tags: string;
+  onTagsChange: (tags: string) => void;
+  limits: ForumLimitsPublic;
+}
+
+/**
+ * 发帖页发布设置模块：帖子类型、板块、标签三行配置。
+ * 受控组件，所有状态由父级持有。
+ */
+export default function ComposeContextBar({
+  isEdit,
+  postType,
+  onPostTypeChange,
+  boards,
+  boardId,
+  onBoardChange,
+  tags,
+  onTagsChange,
+  limits,
+}: Props) {
+  return (
+    <section className="compose-context" aria-label="发布设置">
+      <div className="compose-context-row">
+        <span className="compose-context-label">类型</span>
+        <div className="compose-type-field">
+          <div className="compose-type-pills" role="radiogroup" aria-label="帖子类型">
+            <button
+              type="button"
+              role="radio"
+              aria-checked={postType === 'normal'}
+              className={`compose-type-pill${postType === 'normal' ? ' active' : ''}`}
+              onClick={() => onPostTypeChange('normal')}
+            >
+              讨论
+            </button>
+            <button
+              type="button"
+              role="radio"
+              aria-checked={postType === 'question'}
+              className={`compose-type-pill${postType === 'question' ? ' active' : ''}`}
+              onClick={() => onPostTypeChange('question')}
+            >
+              问答
+            </button>
+          </div>
+          {postType === 'question' && (
+            <span className="compose-type-hint">问答可标记解决状态</span>
+          )}
+        </div>
+      </div>
+      <div className="compose-context-row">
+        <span className="compose-context-label">板块</span>
+        <div
+          className="compose-board-pills"
+          role="listbox"
+          aria-label={isEdit ? '修改板块' : '选择板块'}
+        >
+          {boards.map(b => {
+            const themeIdx = getBoardThemeIndex(b);
+            const isActive = String(b.id) === boardId;
+            return (
+              <button
+                key={b.id}
+                type="button"
+                role="option"
+                aria-selected={isActive}
+                className={`compose-board-pill compose-board-pill--${themeIdx}${isActive ? ' active' : ''}`}
+                onClick={() => onBoardChange(String(b.id))}
+              >
+                <BoardIconDisplay
+                  board={b}
+                  className="compose-board-icon"
+                />
+                <span>{b.name}</span>
+              </button>
+            );
+          })}
+        </div>
+      </div>
+      <div className="compose-context-row compose-context-row--tags">
+        <span className="compose-context-label">标签</span>
+        <TagInput
+          value={tags}
+          onChange={onTagsChange}
+          placeholder="添加标签，回车确认"
+          maxLength={limits.post_tags_max > 0 ? limits.post_tags_max : undefined}
+        />
+      </div>
+    </section>
+  );
+}