style CallButton to match SendButton — accent gradient, press animation

Same 38dp circle as SendButton. Subtle accent gradient fill (16-28%
alpha), AudioLines icon in accent.primary color, press-scale animation.
Visually pairs with the send button as its idle counterpart.

app/src/main/java/dev/kaizen/app/chat/ChatComponents.kt

@@ -593,12 +593,7 @@ fun ChatInput(
                 if (hasContent) {
                     SendButton(enabled = canSend, onClick = onSend)
                 } else {
-                    Box(
-                        Modifier.size(38.dp).clip(KaizenShapes.circle).background(iconBg),
-                        contentAlignment = Alignment.Center,
-                    ) {
-                        Icon(KaizenIcons.AudioLines, stringResource(R.string.chat_call), tint = cs.onSurfaceVariant, modifier = Modifier.size(19.dp))
-                    }
+                    CallButton(onClick = { /* TODO: call feature */ })
                 }
             }
         }
@@ -678,6 +673,35 @@ private fun SendButton(enabled: Boolean, onClick: () -> Unit) {
     }
 }
 
+@Composable
+private fun CallButton(onClick: () -> Unit) {
+    val cs = MaterialTheme.colorScheme
+    val isDark = isSystemInDarkTheme()
+    val interaction = remember { MutableInteractionSource() }
+    val pressed by interaction.collectIsPressedAsState()
+    val pressScale by animateFloatAsState(if (pressed) 0.88f else 1f, label = "call")
+    val accent = LocalKaizenAccent.current
+
+    Box(
+        Modifier
+            .size(38.dp)
+            .scale(pressScale)
+            .clip(KaizenShapes.circle)
+            .background(
+                Brush.verticalGradient(
+                    listOf(
+                        accent.primary.copy(alpha = if (isDark) 0.22f else 0.16f),
+                        accent.primaryDeep.copy(alpha = if (isDark) 0.28f else 0.22f),
+                    )
+                )
+            )
+            .clickable(interactionSource = interaction, indication = null, onClick = onClick),
+        contentAlignment = Alignment.Center,
+    ) {
+        Icon(KaizenIcons.AudioLines, null, tint = accent.primary, modifier = Modifier.size(19.dp))
+    }
+}
+
 // ── Attachment rendering ────────────────────────────────────────────────────
 
 private object NetworkImageCache {