feat: Dashboard数据关联修复 + 通知模板优化 + 工单创建页布局

1. Dashboard: stats新增queryStats查询统计, trend API真实工单趋势数据
2. Layout铃铛: 显示真实待审批工单数量
3. 通知模板优化:
   - 创建工单通知: 含申请人+目标实例+库+SQL摘要
   - 审批通过/拒绝通知: 含审批人+目标实例
   - 执行完成/失败通知: 含执行人+目标实例+库
4. 飞书卡片颜色: 创建=turquoise, 审批=blue, 成功=green, 失败=red
5. 钉钉消息: 添加状态emoji标签(🆕✅❌⚠️)
6. TicketCreatePage: 底部操作栏(SQL检测+提交审批)
7. ticket_executor: 移除aiomysql不支持的read_timeout/write_timeout

Tests: 1057 passed, 17 pre-existing failures (notification 35/35 passed)

backend/app/schemas/dashboard.py

@@ -1,5 +1,12 @@
 from pydantic import BaseModel
-from typing import Optional
+from typing import Optional, List
+
+
+class QueryStatsData(BaseModel):
+    total: int = 0
+    avg_time_ms: int = 0
+    slow_count: int = 0
+    type_distribution: List[dict] = []
 
 
 class DashboardStats(BaseModel):
@@ -11,3 +18,15 @@ class DashboardStats(BaseModel):
     instance_online: int = 0
     user_total: int = 0
     queries_today: int = 0
+    query_stats: Optional[QueryStatsData] = None
+
+
+class TrendPoint(BaseModel):
+    date: str
+    submitted: int = 0
+    success: int = 0
+    failed: int = 0
+
+
+class TrendData(BaseModel):
+    items: List[TrendPoint] = []