fix(playwright): hoist SLOW_TEST budget to describe.configure and bump QUERY_EXECUTION

`test.setTimeout()` inside the test body does not apply to fixture
setup — the `dashboardListPage`/`datasetListPage` navigation runs
under the default 30s test budget and times out on slow /app/prefix
CI starts. Moving the timeout onto `test.describe.configure` extends
it to fixture setup too.

QUERY_EXECUTION bumped 15s → 30s. Cold-start /app/prefix CI has been
observed running trivial `SELECT 1` queries in ~25s before results
render, exceeding both `executeQuery`'s `waitForPost` budget and
`waitForQueryResults`'s `.ant-steps` hidden wait.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>