fix: allow default database for tree-schema databases

TREE_SCHEMA mode databases (saphana, jdbc, postgres, etc.) use an empty string to represent the default database selection. The previous check treated empty string as no database selected and incorrectly blocked query execution.

apps/desktop/src/composables/useSqlExecution.ts

@@ -5,7 +5,7 @@ import { useHistoryStore } from "@/stores/historyStore";
 import { useConnectionStore } from "@/stores/connectionStore";
 import { useSettingsStore } from "@/stores/settingsStore";
 import { useToast } from "@/composables/useToast";
-import { isSingleDatabase } from "@/lib/database/databaseCapabilities";
+import { isSingleDatabase, usesTreeSchemaMode } from "@/lib/database/databaseCapabilities";
 import { canExecuteWithoutSelectedDatabase } from "@/lib/connection/connectionLevelDatabaseBootstrap";
 import { classifySqlActivityKind } from "@/lib/history/historyActivityKind";
 import { sqlMetadataRefreshTarget } from "@/lib/sql/sqlMetadataRefresh";
@@ -229,7 +229,9 @@ function supportsSqlTemplateParameters(connection: ConnectionConfig | undefined)
 
 export function requiresDatabaseSelection(tab: QueryTab, connection: ConnectionConfig | undefined, sql = ""): boolean {
   if (tab.mode !== "query") return false;
-  if (!connection || tab.database) return false;
+  if (!connection) return false;
+  if (tab.database) return false;
+  if (tab.database === "" && usesTreeSchemaMode(connection.db_type)) return false;
   if (isSingleDatabase(connection.db_type)) return false;
   if (canExecuteWithoutSelectedDatabase(connection, sql)) return false;
   return !["elasticsearch", "qdrant", "milvus", "weaviate", "chromadb", "zookeeper"].includes(connection.db_type);