feat(sign_in): 新增独立每日签到插件，与抽卡签到共用同一份签到数据

- 群聊命令「签到」(别名: 每日签到/打卡)，白名单群聊或管理员可用
- 复用 xapi /bot/gacha/sign-in + /bot/points/add，与抽卡/WPF 共用 bot_gacha_daily_sign_in 表
- 积分随机 1-100，流水沿用 gacha_sign/抽卡签到；先到先得，重复签到提示已签到
- 新增 10 个单元测试，ruff 通过；更新 PLUGINS.md / README.md

danding_bot/plugins/danding_sign_in/service.py

@@ -0,0 +1,66 @@
+"""独立签到插件 - 签到编排。
+
+先记录签到再发放积分（与抽卡签到 `onmyoji_gacha/sign_in.py` 同模式），
+避免重复签到时重复发积分：xapi `POST /bot/gacha/sign-in` 负责判断当天
+是否已签到（与抽卡/WPF 共用 `bot_gacha_daily_sign_in` 表去重），只有它
+确认首次签到后，才调用 `/bot/points/add` 发积分。
+"""
+
+from __future__ import annotations
+
+import logging
+import random
+from typing import Any, Dict, Optional, Protocol
+
+logger = logging.getLogger(__name__)
+
+
+class SignInRecorder(Protocol):
+    async def record_sign_in(self, user_id: str, points_awarded: int) -> Optional[Dict[str, Any]]:
+        """记录每日签到，返回 xapi data（含 signed_already）；失败返回 None。"""
+
+
+class PointsAwarder(Protocol):
+    async def add_points(self, user_id: str, amount: int, source: str, reason: str) -> tuple[bool, int]:
+        """发放积分，返回（是否成功, 新余额）。"""
+
+
+async def perform_daily_sign_in(
+    *,
+    sign_in_api: SignInRecorder,
+    points_api: PointsAwarder,
+    user_id: str,
+    points_min: int,
+    points_max: int,
+    source: str,
+    reason: str,
+) -> Dict[str, Any]:
+    """执行每日签到。
+
+    返回 dict：
+      - {"success": True, "already_signed": False, "points": int, "balance": int}  首次签到成功
+      - {"success": True, "already_signed": True, "points": int, "sign_date": str} 当天已签到
+      - {"success": False, "message": str}                                         失败
+    """
+
+    low, high = sorted((points_min, points_max))
+    points = random.randint(low, high)
+
+    sign_result = await sign_in_api.record_sign_in(user_id, points)
+    if sign_result is None:
+        return {"success": False, "message": "签到服务暂不可用，请稍后再试"}
+
+    if sign_result.get("signed_already"):
+        # 今天已签到（抽卡/WPF/命令任一入口先到先得），不重复发积分
+        return {
+            "success": True,
+            "already_signed": True,
+            "points": int(sign_result.get("points_awarded", 0) or 0),
+            "sign_date": str(sign_result.get("sign_date", "")),
+        }
+
+    ok, balance = await points_api.add_points(user_id, points, source, reason)
+    if not ok:
+        logger.error("签到记录成功但积分发放失败 user_id=%s points=%s", user_id, points)
+        return {"success": False, "message": "积分发放失败，请稍后再试"}
+    return {"success": True, "already_signed": False, "points": points, "balance": balance}