Harden UI layout for font scale and long strings

- Measure and cap the HUD target chip after each font-scale change; clip HUD top labels.
- Ellipsize long action-button labels so panels cannot grow past the viewport.
- Add accessibility/button layout assertions and refresh the gallery captures.
- Record the font/layout pass in TODO, docs, changelog and memory.

src/test/tests/test_ui_buttons.gd

@@ -23,8 +23,12 @@ func test_shared_button_states_are_complete() -> bool:
 	var c := TestUtils.check(disabled != null and normal != null
 		and disabled.bg_color != normal.bg_color,
 		"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,
+		"long action labels ellipsize instead of forcing a wide panel")
 	button.free()
-	return a and b and c
+	return a and b and c and d
 
 func test_focus_helper_skips_hidden_and_disabled_controls() -> bool:
 	var hidden := Button.new()