fix: 头像缓存版本号；移除回忆录撰写入口跳转聊天

- API：上传/预设头像 URL 追加 ?v=time.time_ns()，避免同路径缓存导致「只能换一次头像」
- Expo：回忆录 Tab 去掉撰写中「继续写作」及新建会话跳转；清理 memoir 文案键并更新 i18n 类型

未纳入提交：本地 api/uploads/（开发环境头像文件）

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

api/app/features/auth/router.py

@@ -1,4 +1,5 @@
 import io
+import time
 from pathlib import Path
 
 from fastapi import APIRouter, Depends, File, HTTPException, UploadFile, status
@@ -331,7 +332,8 @@ async def upload_avatar(
 
         image.save(file_path, "JPEG", quality=85, optimize=True)
 
-        avatar_url = f"/api/auth/avatars/{filename}"
+        # 路径固定为 {user_id}.jpg，客户端会缓存；每次写入新文件后 bump URL 以绕过缓存。
+        avatar_url = f"/api/auth/avatars/{filename}?v={time.time_ns()}"
         user = await service.update_avatar_url(current_user.id, avatar_url)
         return _user_response(user)
     except HTTPException:
@@ -379,7 +381,7 @@ async def set_avatar_preset(
             status_code=status.HTTP_400_BAD_REQUEST,
             detail="预设头像不可用",
         )
-    avatar_url = avatar_url_for_preset_filename(filename)
+    avatar_url = f"{avatar_url_for_preset_filename(filename)}?v={time.time_ns()}"
     try:
         user = await service.update_avatar_url(current_user.id, avatar_url)
     except AuthError as e: