feat: add GaussDB ODBC support and flatten connection list

- Add GaussDB/openGauss support via ODBC (resolves #106)
- Use pg_catalog queries instead of information_schema for compatibility
- Share ODBC environment across drivers with auto ODBCSYSINI detection
- Fix ODBC error message false positive on "Driver" keyword match
- Merge connection dialog categories into a single flat list
- Remove duplicate DDL button from data grid footer

src/lib/tableSelectSql.ts

@@ -26,7 +26,8 @@ export function qualifiedTableName(
     (databaseType === "postgres" ||
       databaseType === "oracle" ||
       databaseType === "sqlserver" ||
-      databaseType === "dameng") &&
+      databaseType === "dameng" ||
+      databaseType === "gaussdb") &&
     schema
   ) {
     return `${quoteTableIdentifier(databaseType, schema)}.${quoteTableIdentifier(databaseType, tableName)}`;