fix(studio): escape SQL identifiers in row export

Discovered a bug in `formatTableRowsToSQL`: schema, table, and column names are wrapped in double quotes but embedded double quotes are not escaped. PostgreSQL permits identifiers containing `"`, so Copy as SQL / Export as SQL can generate invalid SQL for valid table or column names. Example table name: `customer"name` currently produces invalid SQL instead of quoting the identifier correctly. A narrow fix is to escape `"` as `""` when quoting PostgreSQL identifiers and add regression coverage for schema/table/column names containing double quotes.