feat(ui): format system init message in StreamLineFormatter

src/ClaudeDo.Ui/Helpers/StreamLineFormatter.cs

@@ -43,11 +43,30 @@ public class StreamLineFormatter
     {
         if (!root.TryGetProperty("subtype", out var subtypeProp))
             return null;
-        return subtypeProp.GetString() switch
+
+        var subtype = subtypeProp.GetString();
+        switch (subtype)
         {
-            "api_retry" => "[Retrying API call...]\n",
+            case "api_retry":
-            _           => null,
+                return "[Retrying API call...]\n";
-        };
+
+            case "init":
+            {
+                var sessionId = root.TryGetProperty("session_id", out var sid)
+                    ? sid.GetString() : null;
+                var model = root.TryGetProperty("model", out var m)
+                    ? m.GetString() : null;
+
+                var shortId = sessionId is { Length: >= 8 }
+                    ? sessionId[..8]
+                    : sessionId ?? "?";
+                var modelPart = string.IsNullOrEmpty(model) ? "" : $" · {model}";
+                return $"[session {shortId}{modelPart}]\n";
+            }
+
+            default:
+                return null;
+        }
     }
 
     private static string? FormatAssistant(JsonElement root) => null;