Ship the 0.9.0 production-quality milestone

Add mixer/accessibility settings, caption/reduce-motion hooks, audio volume
clamping, a 24-NPC performance smoke and shortened coat/dress stride for hem
clipping. Record the explicit Godot 4.3-CI/4.7-local matrix and the 0.9
production scope. Headless 250/250, Python 94/94, 24-NPC budget smoke passes.

src/test/tests/test_persistence.gd

@@ -81,7 +81,9 @@ func test_settings_defaults_present() -> bool:
 	var ok := TestUtils.check(
 		defaults.has("look_sensitivity") and defaults.has("hud_font_scale")
 			and defaults.has("invert_y") and defaults.has("head_bob")
-			and defaults.has("input_bindings"),
+			and defaults.has("input_bindings")
+		and defaults.has("master_volume") and defaults.has("sfx_volume")
+		and defaults.has("ambience_volume") and defaults.has("captions_enabled"),
 		"settings have documented defaults")
 	save.free()
 	return ok