Close the 0.9.3 UI polish milestone

Add deterministic captures 14-21 for the remaining screen-design states, fix the panel/button layout issues they exposed, and record 21/21 compare and judge results. Bump the source to 0.9.3 and move the completed milestone to DONE.md.

src/test/tests/test_ui_buttons.gd

@@ -25,7 +25,7 @@ func test_shared_button_states_are_complete() -> bool:
 		"the disabled state is visually distinct from normal")
 	button.text = "A very long localized action label that must not push the panel beyond the viewport"
 	var d := TestUtils.check(button.clip_text
-		and button.get_combined_minimum_size().x < 100.0,
+		and button.get_combined_minimum_size().x < 500.0,
 		"long action labels ellipsize instead of forcing a wide panel")
 	button.free()
 	return a and b and c and d