feat: 接线上行帧分发到 message/identity/presence/group

internal/app/presence/encode.go

@@ -0,0 +1,22 @@
+package presence
+
+// EncodeGetData 把 Get 结果编成 presence.get 的 resp data（items 数组）。
+// 未知编号项为 {"id":"...","not_found":true}，其余含 id/online/since_ms。
+func EncodeGetData(items []StatusItem) map[string]any {
+	out := make([]map[string]any, 0, len(items))
+	for _, it := range items {
+		if it.NotFound {
+			out = append(out, map[string]any{
+				"id":        it.ID,
+				"not_found": true,
+			})
+			continue
+		}
+		out = append(out, map[string]any{
+			"id":       it.ID,
+			"online":   it.Online,
+			"since_ms": it.SinceMs,
+		})
+	}
+	return map[string]any{"items": out}
+}