feat: implement WeChat cross-batch refund reconciliation and fix misc issues

WeChat cross-batch refund reconciliation:
- Add OriginalAmount field to CleanedBill for accurate cumulative refund math
- DeduplicateRawFile detects WeChat status-update rows (已退款/已全额退款) and
  emits WechatRefundUpdates for Go-side reconciliation (Scenario 1)
- WechatPy cleaner surfaces -退款 income rows with no same-batch expense match
  as unresolved_refunds for Go ReconcileRefund (Scenario 2)
- Add ReconcileWechatRefund to repository interface and MongoDB implementation
- upload.go step 15 iterates WechatRefundUpdates and reconciles against bills_cleaned

Bug fixes:
- ReviewStats: add nil repo check to prevent panic when DB is not connected
- JWT: remove hardcoded fallback secret; return 500/401 if JWTSecret not configured
- Remove unused parsePageParam dead code and its strconv import
- BillDetailDrawer: show 不计收支 amount in muted gray instead of red
- test_jd_cleaner.py: replace hardcoded D:\Projects\BillAI path with dynamic __file__ resolution

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

analyzer/cleaners/wechat.py

@@ -54,7 +54,23 @@ class WechatCleaner(BaseCleaner):
         
         # 第三步：处理退款（包括转账退款）
         final_expense_rows, income_rows = self._process_refunds(expense_rows, income_rows)
-        
+
+        # 收集跨批次未匹配的 -退款 行（当前批次无对应支出记录，需 Go 侧跨批次核销）
+        expense_merchants = {exp[2].strip() for exp in expense_rows}
+        for refund_row in refund_rows:
+            if refund_row[2].strip() not in expense_merchants:
+                amount = float(parse_amount(refund_row[5]))
+                if amount > 0:
+                    self.unresolved_refunds.append({
+                        "order_no": "",
+                        "merchant_order_no": refund_row[9].strip() if len(refund_row) > 9 else "",
+                        "refund_order_no": refund_row[8].strip() if len(refund_row) > 8 else "",
+                        "amount": amount,
+                        "time": refund_row[0],
+                        "merchant": refund_row[2],
+                        "description": refund_row[3] if len(refund_row) > 3 else "",
+                    })
+
         print(f"\n处理结果:")
         print(f"  全额退款删除: {self.stats['fully_refunded']} 条")
         print(f"  部分退款调整: {self.stats['partially_refunded']} 条")