feat: add admin point grants and history UI

backend/src/main/java/com/openisle/service/PointService.java

@@ -43,6 +43,22 @@ public class PointService {
     return addPoint(user, 500, PointHistoryType.FEATURE, post, null, null);
   }
 
+  public int grantPointByAdmin(String adminName, String targetUsername, int amount) {
+    if (amount <= 0) {
+      throw new FieldException("amount", "积分必须为正数");
+    }
+    if (targetUsername == null || targetUsername.isBlank()) {
+      throw new FieldException("username", "用户名不能为空");
+    }
+    String normalizedUsername = targetUsername.trim();
+    User admin = userRepository.findByUsername(adminName).orElseThrow();
+    User target = userRepository
+      .findByUsername(normalizedUsername)
+      .orElseThrow(() -> new FieldException("username", "用户不存在"));
+    addPoint(target, amount, PointHistoryType.ADMIN_GRANT, null, null, admin);
+    return target.getPoint();
+  }
+
   public void processLotteryJoin(User participant, LotteryPost post) {
     int cost = post.getPointCost();
     if (cost > 0) {