🐛 fix(kingbase): 修复开表与 ER 图加载缓慢问题

- 解耦 Kingbase 首屏查询与编辑定位元数据加载
- 使用单次全库外键快照替代 ER 图逐表扫描
- 补充大规模表结构和异步元数据回归测试

Fixes #731
Fixes #732

internal/db/database.go

@@ -44,6 +44,13 @@ type Database interface {
 	GetTriggers(dbName, tableName string) ([]connection.TriggerDefinition, error)
 }
 
+// DatabaseForeignKeyProvider is an optional metadata interface for drivers that
+// can load a database-wide foreign-key snapshot more efficiently than one table
+// at a time.
+type DatabaseForeignKeyProvider interface {
+	GetDatabaseForeignKeys(dbName string) (map[string][]connection.ForeignKeyDefinition, error)
+}
+
 // TableRowCounter is an optional metadata interface for drivers that can
 // provide exact table row counts alongside a table list.
 type TableRowCounter interface {