UI: Update light and dark surface colors (#557)

### TL;DR
Updated surface colors for both light and dark themes

### What changed?
- Light theme surface color changed from `0xFFFFFBFF` to `0xFFFFFFFF` (slightly whiter)
- Dark theme surface color changed from `0xFF1F1B16` to `0xFF1C1B1A` (slightly darker)

### How to test?
1. Launch the app in both light and dark modes
2. Navigate through different screens
3. Verify the background surface colors appear correct
4. Ensure there's proper contrast between surface and content

### Why make this change?
The surface color adjustments improve visual consistency and maintain better contrast ratios with other theme colors. The light theme now uses pure white for a cleaner look, while the dark theme's adjustment provides better visual comfort in low-light conditions.

taj/src/commonMain/kotlin/xyz/ksharma/krail/taj/theme/Color.kt

@@ -8,7 +8,7 @@ val md_theme_light_error = Color(0xFFBA1A1A)
 val md_theme_light_errorContainer = Color(0xFFFFDAD6)
 val md_theme_light_onError = Color(0xFFFFFFFF)
 val md_theme_light_onErrorContainer = Color(0xFF410002)
-val md_theme_light_surface = Color(0xFFFFFBFF)
+val md_theme_light_surface = Color(0xFFFFFFFF)
 val md_theme_light_onSurface = Color(0xFF1F1B16)
 val md_theme_light_scrim = Color(0xFF000000)
 val md_theme_light_alert = Color(0xFFFFBA27)
@@ -18,7 +18,7 @@ val md_theme_dark_error = Color(0xFFFFB4AB)
 val md_theme_dark_errorContainer = Color(0xFF93000A)
 val md_theme_dark_onError = Color(0xFF690005)
 val md_theme_dark_onErrorContainer = Color(0xFFFFDAD6)
-val md_theme_dark_surface = Color(0xFF1F1B16)
+val md_theme_dark_surface = Color(0xFF1C1B1A)
 val md_theme_dark_onSurface = Color(0xFFEAE1D9)
 val md_theme_dark_scrim = Color(0xFF000000)
 val md_theme_dark_alert = Color(0xFFF4B400)