test(ui): widget and layout tests for the button family and for one height per row #1340

Part of #1331. Continues #1043's approach for the new components.

Scope (test/shared/widgets/)

• querya_button_test.dart: variants x sizes, loading keeps width, disabled, pressed / hover colours from the workbench, keyboard focus ring only for keyboard focus, tooltip delay, semantics.
• querya_split_and_menu_button_test.dart: one height and border, menu open state, keyboard.
• querya_dialog_actions_test.dart: order, spacing, one primary, Esc / Enter.
• querya_control_row_height_test.dart: a row of button, icon button, dropdown, search field and tab strip at each size has one height, at uiScale 0.9 / 1 / 1.25 and text scale 1 / 1.5, with no overflow.
• querya_button_theme_switch_test.dart: switching theme at runtime recolours all variants without a frame in the old colours (as in test(ui): comprehensive widget test suite for Querya UI Kit components #1043).
• Each test works in headless Linux CI.

Acceptance

• The tests above are in core-ui or features-app and stable.
• A reduced-motion run shows no animation in state changes.