ui: fix grey Wownero coin logo + lift too-dark dashboard background

- res/pictures/balance_card_icons/wownero.svg had an opaque background rect
  (+#FFF5FD fill), so the ChainIcon's srcIn colorFilter flooded the whole
  circle solid grey. Replaced with a clean alpha glyph (white W-in-circle on
  transparent, like monero.svg) so the dark bg shows through the negative
  space. Source in res/pictures → compile_graphics.sh regenerates the .vec.
- dark theme surface #0B1F14 → #10281B (a bit less dark, per feedback)

lib/themes/theme_classes/dark_theme.dart

@@ -14,7 +14,7 @@ class DarkTheme extends MaterialThemeBase {
   //  - Primary: mint (#7FCAA0) — light enough to read on dark surface
   //  - Secondary: soft pink (#E16FA6)
   //  - Tertiary: soft blue (#6AB7E6)
-  //  - Surface: deep green (#0B1F14)
+  //  - Surface: deep green (#10281B) — lifted slightly from #0B1F14 (too dark)
   @override
   Color get primaryColor => const Color(0xFF7FCAA0);
 
@@ -25,7 +25,7 @@ class DarkTheme extends MaterialThemeBase {
   Color get errorColor => const Color(0xFFFFB4AB);
 
   @override
-  Color get surfaceColor => const Color(0xFF0B1F14);
+  Color get surfaceColor => const Color(0xFF10281B);
 
   @override
   Color get tertiaryColor => const Color(0xFF6AB7E6);