feat(frontend): darken neutral theme and reorder theme switcher

- make neutral theme a warm dark graphite
- order switches as dark -> neutral -> light -> system
- replace neutral icon with contrast glyph

frontend/src/app.css

@@ -38,22 +38,22 @@
 	--shadow: 0 0% 0% / 0.4;
 }
 
-/* Нейтральная (тёплая серо-бежевая) */
+/* Нейтральная (тёплый графит) */
 [data-theme='neutral'] {
-	--bg: 40 20% 96%;
-	--bg-elevated: 40 22% 92%;
-	--bg-muted: 40 18% 87%;
-	--border: 40 14% 78%;
-	--text: 30 10% 15%;
-	--text-muted: 30 8% 40%;
-	--text-subtle: 30 6% 55%;
-	--primary: 25 90% 50%;
+	--bg: 30 12% 18%;
+	--bg-elevated: 30 12% 23%;
+	--bg-muted: 30 11% 28%;
+	--border: 30 9% 34%;
+	--text: 35 18% 93%;
+	--text-muted: 32 10% 68%;
+	--text-subtle: 30 7% 50%;
+	--primary: 25 90% 55%;
 	--primary-fg: 0 0% 100%;
-	--danger: 0 72% 55%;
-	--success: 142 55% 42%;
-	--chrome: 40 22% 92%;
-	--canvas: 40 20% 96%;
-	--shadow: 30 20% 20% / 0.12;
+	--danger: 0 72% 62%;
+	--success: 142 45% 52%;
+	--chrome: 30 12% 15%;
+	--canvas: 30 12% 18%;
+	--shadow: 30 30% 5% / 0.45;
 }
 
 html,