fix(profile): tint the cashu chip icon and brighten its purple

The Cashu vector is a monochrome black outline meant to be tinted like a
Material Symbol — with Color.Unspecified it rendered black and vanished
on dark backgrounds. Tint it with the chip color and lift the purple
from 0xFF7E57C2 to 0xFFA855F7 so the chip reads on both themes.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/profile/header/ProfilePaymentRailChips.kt

@@ -66,7 +66,7 @@ import com.vitorpamplona.amethyst.ui.theme.Size16Modifier
 import kotlinx.coroutines.launch
 import androidx.compose.material3.Icon as M3Icon
 
-private val CashuPurple = Color(0xFF7E57C2)
+private val CashuPurple = Color(0xFFA855F7)
 
 /**
  * One FlowRow of tappable chips for every rail the Send Payment screen can pay
@@ -159,10 +159,13 @@ fun DisplayPaymentRailChips(
                 label = stringRes(R.string.send_payment_method_cashu),
                 onClick = { openSendPayment(ProfilePaymentMethod.CASHU) },
             ) {
+                // The Cashu vector is a monochrome outline drawn in black,
+                // meant to be tinted like a Material Symbol — untinted it
+                // disappears on dark backgrounds.
                 M3Icon(
                     imageVector = CustomHashTagIcons.Cashu,
                     contentDescription = null,
-                    tint = Color.Unspecified,
+                    tint = CashuPurple,
                     modifier = Size16Modifier,
                 )
             }