feat(onboarding): 新手引导完成按 设备+账号 去重(表/模型/仓储/端点/迁移/测试)

- onboarding_completion 表(user_id+device_id 唯一约束)+ model + repository
- POST /api/v1/user/onboarding/complete 标记完成;登录响应 TokenWithUser.onboarding_completed
  (按登录请求带的 device_id 判定是否已走过引导,跨卸载重装稳定)
- alembic 迁移 onboarding_completion(rebase 到最新 main 后已链在 coupon_daily_completion 之后,单 head)
- docs/database 文档 + tests/test_onboarding.py + run.bat(本地启动脚本)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/api/v1/user.py

@@ -16,9 +16,10 @@ from fastapi import APIRouter, File, HTTPException, UploadFile
 
 from app.api.deps import CurrentUser, DbSession
 from app.core import media
+from app.repositories import onboarding as onboarding_repo
 from app.repositories import user as user_repo
 from app.schemas.auth import UserOut
-from app.schemas.user import OkResponse, ProfileUpdateRequest
+from app.schemas.user import OkResponse, OnboardingCompleteRequest, ProfileUpdateRequest
 
 logger = logging.getLogger("shagua.user")
 
@@ -51,6 +52,17 @@ async def upload_avatar(
     return UserOut.model_validate(updated)
 
 
+@router.post("/onboarding/complete", response_model=OkResponse, summary="标记新手引导完成(按 设备+账号)")
+def complete_onboarding(
+    req: OnboardingCompleteRequest, user: CurrentUser, db: DbSession
+) -> OkResponse:
+    """走完新手引导时调一次。按 (当前账号, device_id) 落一条完成标记,跨卸载重装持久。
+    幂等:重复调用不报错。device_id 取客户端硬件级 ANDROID_ID,与登录请求一致。"""
+    onboarding_repo.mark_completed(db, user_id=user.id, device_id=req.device_id)
+    logger.info("onboarding complete user_id=%d device_len=%d", user.id, len(req.device_id))
+    return OkResponse()
+
+
 @router.delete("", response_model=OkResponse, summary="注销账号(软删除)")
 def delete_account(user: CurrentUser, db: DbSession) -> OkResponse:
     media.delete_avatar(user.avatar_url)