feat: Bot API L1-L4风险分级标注 + 操作审计日志

- 新增 app/risk_levels.py: RISK_LEVELS定义 + @risk_level装饰器 + API_RISK_MAP
  (L1只读21 / L2业务写5 / L3批量写3 / L4=0安全底线)
- 新增 app/api/audit_log.py: Bot API审计中间件 → backend/logs/bot_audit.log
  (JSON行: timestamp/bot_name/endpoint/method/risk_level/entity_id/status,
   L3额外记rows行数, 不阻塞业务)
- bot_bridge/bot_bridge_v2/bot_kpis/bot_iron_law 全部29路由标注级别
- 新增 GET /api/cma/bot/risk-levels (X-BOT-KEY鉴权): API→级别→处理方式清单
- main.py 注册审计中间件
- tests/test_risk_levels.py: 覆盖路由标注/risk-levels端点/L4不存在/审计日志

backend/app/api/bot_kpis.py

@@ -7,6 +7,7 @@ from datetime import datetime
 from app.database import get_db
 from app.auth_middleware import require_auth
 from app.models import KPIDefinition, KPIValue
+from app.risk_levels import risk_level
 
 router = APIRouter(prefix="/api/cma/bot-kpis", tags=["Bot KPI管理"],
     dependencies=[Depends(require_auth)],
@@ -46,6 +47,7 @@ def _calc_bot_kpi_score(current_value, target_value, is_reverse=False):
 
 
 @router.get("")
+@risk_level("L1")
 def list_bot_kpis(
     source: str = Query("finance-bot", description="Bot标识"),
     period: Optional[str] = None,
@@ -132,6 +134,7 @@ def list_bot_kpis(
 
 
 @router.post("/{kpi_id}/value")
+@risk_level("L2")
 def update_bot_kpi_value(
     kpi_id: int,
     data: dict,