feat: add dark mode styling for combat values and text strokes

Use CSS filters and light-dark() function for theme-adaptive icons and
text styling with proper contrast in both light and dark modes.

scss/components/actor/_combat_value.scss

@@ -74,10 +74,10 @@
 
 // Dark mode filter for combat value backgrounds when in dark theme
 .theme-dark .ds4-combat-value__value {
-  filter: invert(1);
+  filter: brightness(0) invert(1) brightness(0.8);
 
   // Counter-invert the text to keep it normal
   .ds4-combat-value__text {
-    filter: invert(1);
+    filter: brightness(1.25) invert(1) brightness(0.8);
   }
 }