fix(ui): leave an avatar with no name as the bare gradient

InitialsText fell back to "?" when the name had no letters. It now
draws nothing, matching iOS, which shows only the gradient.

Author: bmc08gt

apps/flipcash/shared/common-ui/src/main/kotlin/com/flipcash/shared/common/ui/ContactAvatar.kt

@@ -331,8 +331,9 @@ private fun BoxWithConstraintsScope.InitialsText(displayName: String) {
             .take(2)
             .mapNotNull { it.firstOrNull()?.uppercaseChar() }
             .joinToString("")
-            .ifEmpty { "?" }
     }
+    // A name with no letters leaves the gradient on its own, as iOS does, rather than a "?".
+    if (initials.isEmpty()) return
     val fontSize = with(LocalDensity.current) {
         (min(maxWidth, maxHeight) * 0.38f).toSp()
     }