修复无板块时空态导航失效，去除发帖本地草稿，并种子默认板块。

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

frontend/src/utils/composeDraft.ts

@@ -1,61 +0,0 @@
-export interface ComposeDraft {
-  title: string;
-  tags: string;
-  content: string;
-  boardId: string;
-  savedAt: number;
-}
-
-const PREFIX = 'j13-compose-draft:';
-
-function draftKey(editId: number | null): string {
-  return editId == null ? `${PREFIX}new` : `${PREFIX}edit:${editId}`;
-}
-
-/** 读取发帖/编辑草稿 */
-export function loadComposeDraft(editId: number | null): ComposeDraft | null {
-  try {
-    const raw = localStorage.getItem(draftKey(editId));
-    if (!raw) return null;
-    const data = JSON.parse(raw) as ComposeDraft;
-    if (!data || typeof data !== 'object') return null;
-    return {
-      title: typeof data.title === 'string' ? data.title : '',
-      tags: typeof data.tags === 'string' ? data.tags : '',
-      content: typeof data.content === 'string' ? data.content : '',
-      boardId: typeof data.boardId === 'string' ? data.boardId : '',
-      savedAt: typeof data.savedAt === 'number' ? data.savedAt : 0,
-    };
-  } catch {
-    return null;
-  }
-}
-
-/** 写入发帖/编辑草稿 */
-export function saveComposeDraft(editId: number | null, draft: Omit<ComposeDraft, 'savedAt'>): void {
-  try {
-    const payload: ComposeDraft = { ...draft, savedAt: Date.now() };
-    localStorage.setItem(draftKey(editId), JSON.stringify(payload));
-  } catch {
-    // 配额不足等场景静默忽略
-  }
-}
-
-/** 清除发帖/编辑草稿 */
-export function clearComposeDraft(editId: number | null): void {
-  try {
-    localStorage.removeItem(draftKey(editId));
-  } catch {
-    // ignore
-  }
-}
-
-/** 草稿是否相对 baseline 有实质内容 */
-export function draftHasContent(draft: ComposeDraft): boolean {
-  return Boolean(
-    draft.title.trim()
-    || draft.tags.trim()
-    || draft.content.trim()
-    || draft.boardId.trim(),
-  );
-}