feat(analytics): A3 流失预警三分法——真流失/从未激活/待交接

Co-Authored-By: Claude Code <noreply@anthropic.com>

yunke-server/app/api/routers/analytics.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 
 from typing import Annotated, Any, Literal
 
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.analytics import health as health_svc
@@ -36,3 +36,22 @@ async def analytics_overview(
     与 entities[].last_seen 为 ISO 字符串的双格式)。
     """
     return await metrics_svc.overview(session, channel=channel, scope=scope)
+
+
+@router.get("/churn")
+async def churn_list(
+    session: SessionDep,
+    channel: ChannelParam = "wechat",
+    type: Literal["real", "inactive", "handover"] = "real",
+    tier: int = Query(30, ge=30, le=90),
+    min_msgs: int = Query(5, ge=1, le=100),
+    page: int = Query(1, ge=1),
+    page_size: int = Query(20, ge=1, le=100),
+) -> dict[str, Any]:
+    """A3 流失预警名单(三分法)。tier 只认 30/60/90。"""
+    if tier not in (30, 60, 90):
+        raise HTTPException(422, "tier must be 30/60/90")
+    return await metrics_svc.churn(
+        session, channel=channel, kind=type, tier=tier,
+        min_msgs=min_msgs, page=page, page_size=page_size,
+    )