test: CMA自动化测试补覆盖 226→452用例, 覆盖率36%→60%

- 新增8个测试文件(bot_bridge/kpi_causality/cash/predict/reports/tax_compliance/expenses/probe_cost)
- 增强 budget/auth/users + conftest账套模式适配
- 测试驱动修复: bot_bridge导入batch_id→source_batch; cash_forecast extra空dict
- 全量: 451 passed, 1 xfailed; 报告 docs/cma-test-coverage-report.md

backend/app/api/bot_bridge.py

@@ -529,7 +529,7 @@ def bot_import_excel(
                 continue
             
             kv = KPIValue(kpi_id=kpi.id, period=period, actual_value=val,
-                          batch_id=hashlib.md5(f"{datetime.now()}".encode()).hexdigest()[:12])
+                          source_batch=hashlib.md5(f"{datetime.now()}".encode()).hexdigest()[:12])
             db.add(kv)
             count += 1
         except Exception as e: