feat(files): add per-channel storage quota [CI]

server/src/WebDrop.Core/Settings.cs

@@ -8,6 +8,8 @@ public sealed class ServerLimits
     public int MaxPayloadBytes { get; set; } = (1 << 20) + 16;
     public int MaxFramesPerItem { get; set; } = 65_536;
     public long MaxChannelBytes { get; set; } = 1L << 30;
+    public long MaxWorkspaceBytes { get; set; } = 1L << 40;
+    public long MaxWorkspaceChannelBytes { get; set; } = 10L << 30;
     /// <summary>最大账号成员数。属性名和 info 字段保持旧线格式兼容。</summary>
     public int MaxSeats { get; set; } = 64;
     public int MaxVisitors { get; set; } = 10_000;