fix(funds): 加固转账冲正、结算收付幂等与坏账核销

- 转入 main_site_timeout 等不可冲正场景直接拒绝，避免假结案
- payment_records / settlement_adjustments 增加 partial unique 索引
- 坏账核销行锁 + meta 幂等回放；补差单记录 result_bill_id
- 新增 FundOperationsHardeningTest 覆盖关键路径

app/Support/DatabaseUniqueViolation.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Support;
+
+use Illuminate\Database\QueryException;
+
+/** 识别数据库唯一约束冲突（PostgreSQL / SQLite / MySQL）。 */
+final class DatabaseUniqueViolation
+{
+    public static function matches(QueryException $e): bool
+    {
+        $sqlState = (string) $e->getCode();
+        $errorInfo = $e->errorInfo ?? null;
+        $driverCode = is_array($errorInfo) ? (int) ($errorInfo[1] ?? 0) : 0;
+
+        if ($sqlState === '23505' || $sqlState === '23000' || $sqlState === '19') {
+            return true;
+        }
+
+        if ($driverCode === 19 || $driverCode === 1062) {
+            return true;
+        }
+
+        return stripos($e->getMessage(), 'unique') !== false;
+    }
+}