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/autoload/save.gd

@@ -78,6 +78,11 @@ const DEFAULT_SETTINGS := {
 	"ai_difficulty": "normal",
 	"tutorial_completed": false,
 	"tutorial_skipped": false,
+	"master_volume": 1.0,
+	"sfx_volume": 1.0,
+	"ambience_volume": 1.0,
+	"reduce_motion": false,
+	"captions_enabled": true,
 }
 
 ## Load player settings, merged over the defaults. Returns a Dictionary.