Add admin user email management

backend/app/routers/admin.py

@@ -1358,6 +1358,35 @@ async def update_user_role(username: str, payload: Dict[str, Any]) -> Dict[str,
     return {"status": "ok", "username": username, "role": role}
 
 
+@router.post("/users/{username}/email")
+async def update_user_email(username: str, payload: Dict[str, Any]) -> Dict[str, Any]:
+    user = get_user_by_username(username)
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+    if not isinstance(payload, dict):
+        raise HTTPException(status_code=400, detail="Invalid payload")
+
+    email = _optional_recipient_email(payload.get("email"))
+    if email:
+        duplicate = next(
+            (
+                candidate
+                for candidate in get_all_users()
+                if str(candidate.get("username") or "").casefold() != username.casefold()
+                and str(candidate.get("email") or "").strip().casefold() == email.casefold()
+            ),
+            None,
+        )
+        if duplicate:
+            raise HTTPException(status_code=409, detail="That email address is already assigned to another user")
+
+    if not set_user_email(username, email):
+        raise HTTPException(status_code=404, detail="User not found")
+    refreshed = get_user_by_username(username)
+    logger.info("Admin updated user contact email: username=%s email_set=%s", username, bool(email))
+    return {"status": "ok", "user": refreshed, "email": email}
+
+
 @router.post("/users/{username}/auto-search")
 async def update_user_auto_search(username: str, payload: Dict[str, Any]) -> Dict[str, Any]:
     enabled = payload.get("enabled") if isinstance(payload, dict) else None