feat: Phase2影响分析 — EXPLAIN预检+大表检测(简化版)+执行策略+风险评估table_sizes支持 (1141测试)

新增:
- explain_preview.py: EXPLAIN预检服务(MySQL/PG), 影响行数预估, 全表扫描检测
- ticket.executor: 三种执行策略(stop_on_error/continue/transaction)
- risk_evaluator: table_sizes参数, 大表ALTER/UPDATE/DELETE自动升级high
- test_phase2_features.py: 22个测试(EXPLAIN+执行策略+大表检测)

简化:
- 砍掉CTX-001上下文感知规则(复杂二次扫描), 合并大表检测到risk_evaluator
- 审核引擎保持纯静态分析, 不再导入_RULE_REGISTRY做二次扫描

模型:
- Ticket加exec_strategy字段
- TicketSqlItem模型
- schema加sql_type/exec_strategy/risk_level/workflow_id

backend/app/api/v1/endpoints/ticket.py

@@ -498,10 +498,25 @@ async def create_ticket(
     # 3. 验证工单内容安全性
     _validate_ticket_content(data)
 
+    # 3.5 EXPLAIN 预检（大表检测合并到 risk_evaluator，不再单独查表大小）
+    table_sizes = {}
+    explain_warnings = []
+    try:
+        from app.services.explain_preview import run_explain_preview
+        import asyncio as _asyncio
+        explain_result = await _asyncio.wait_for(
+            run_explain_preview(data.sql_content, instance, data.target_database),
+            timeout=8.0,
+        )
+        explain_warnings = explain_result.warnings
+        table_sizes = explain_result.table_sizes or {}
+    except Exception as e:
+        import asyncio as _asyncio
+        logger.warning("EXPLAIN 预检失败(非致命): %s", e)
+
     # 4. 自动审核 SQL（带超时保护）
     env = "production" if instance.env == "production" else "development"
     v2_engine = SQLAuditEngineV2(db_session=db, env=env)
-    import asyncio as _asyncio
     try:
         v2_report = await _asyncio.wait_for(
             v2_engine.audit(data.sql_content, db_type=data.db_type, instance_id=data.instance_id),
@@ -525,8 +540,13 @@ async def create_ticket(
         sql_type=data.sql_type or "",
         audit_findings=audit_findings_raw,
         statement_count=len(stmt_list),
+        table_sizes=table_sizes,
     )
 
+    # EXPLAIN 结果可能升级风险等级
+    if explain_warnings and risk_level == "low":
+        risk_level = "medium"
+
     # 6. 匹配审批流 — 优先按 instance.workflow_id，其次按 risk_level 匹配默认流
     workflow = None
     if instance.workflow_id:
@@ -560,6 +580,7 @@ async def create_ticket(
         priority=data.priority,
         risk_level=risk_level,
         workflow_id=workflow.id if workflow else None,
+        exec_strategy=data.exec_strategy or "stop_on_error",
         applicant_id=current_user.id,
         status=initial_status,
         audit_result=json.dumps(v2_report.to_dict(), ensure_ascii=False) if v2_report and v2_report.findings else None,