feat: 审核规则持久化到DB + 全面配置去硬编码化

- AuditRule模型: 新增code/config_json字段，支持规则编码和阈值参数持久化
- audit_engine_v2: _load_rules从DB读config_json覆盖默认config
- audit_rule_sync: 启动时自动从_RULE_REGISTRY同步规则到DB(239条)
- settings API: update后刷新query_service配置缓存
- query_service: MAX_ROWS/QUERY_TIMEOUT/MAX_QUERY_LENGTH/MAX_RESULT_MEMORY改为动态读取system_settings
- ticket_executor: SQL_TIMEOUT/REDIS_TIMEOUT/MONGO_TIMEOUT改为动态获取
- settings_seeds: 新增executor分组(sql/redis/mongo超时) + query_result_max_memory_mb
- audit_rule endpoint: 移除无效的AuditEngine缓存清理（每次audit是新实例）
- 测试: 1057 passed（修复所有新引入失败，17个历史遗留）

backend/app/schemas/audit_rule.py

@@ -4,6 +4,7 @@ from typing import Optional, Literal
 
 
 class AuditRuleCreate(BaseModel):
+    code: Optional[str] = Field(default=None, max_length=50)
     name: str = Field(..., min_length=1, max_length=100)
     description: Optional[str] = None
     rule_type: Literal["syntax", "performance", "safety", "security", "naming", "DDL", "DML", "DQL", "DCL"]
@@ -11,11 +12,13 @@ class AuditRuleCreate(BaseModel):
     db_type: str = "mysql"
     pattern: Optional[str] = None
     value: Optional[str] = Field(default=None, max_length=255)
+    config_json: Optional[str] = Field(default=None, description="规则配置JSON，如 {\"max_index\":20}")
     is_enabled: bool = True
     message: str = Field(..., min_length=1, max_length=500)
 
 
 class AuditRuleUpdate(BaseModel):
+    code: Optional[str] = Field(default=None, max_length=50)
     name: Optional[str] = Field(default=None, min_length=1, max_length=100)
     description: Optional[str] = None
     rule_type: Optional[Literal["syntax", "performance", "safety", "security", "naming", "DDL", "DML", "DQL", "DCL"]] = None
@@ -23,12 +26,14 @@ class AuditRuleUpdate(BaseModel):
     db_type: Optional[str] = None
     pattern: Optional[str] = None
     value: Optional[str] = Field(default=None, max_length=255)
+    config_json: Optional[str] = Field(default=None, description="规则配置JSON，如 {\"max_index\":20}")
     is_enabled: Optional[bool] = None
     message: Optional[str] = Field(default=None, min_length=1, max_length=500)
 
 
 class AuditRuleResponse(BaseModel):
     id: int
+    code: Optional[str] = None
     name: str
     description: Optional[str] = None
     rule_type: str
@@ -36,6 +41,7 @@ class AuditRuleResponse(BaseModel):
     db_type: str
     pattern: Optional[str] = None
     value: Optional[str] = None
+    config_json: Optional[str] = None
     is_enabled: bool
     message: str
     created_at: datetime