feat: add /meta command for channel metadata retrieval

- Implemented the `/meta` command to fetch and display channel metadata including room ID, topic, message count, unique user count, estimated size, and protection level.
- Added `ChannelMetaDto` to encapsulate channel metadata.
- Updated `ChannelsController` to handle the new `/meta` endpoint.
- Introduced `UploadLimits` configuration for admin-defined upload size limits for files, images, audio, and avatars.
- Enhanced error handling and user feedback for metadata retrieval.
- Updated documentation to reflect changes in encryption and room metadata.
- Added tests for the new functionality and upload limits.

src/EchoHub.Client/UI/Dialogs/UpdateProgressDialog.cs

@@ -1,61 +0,0 @@
-using Terminal.Gui.App;
-using Terminal.Gui.Views;
-using Terminal.Gui.ViewBase;
-
-namespace EchoHub.Client.UI.Dialogs;
-
-public sealed class UpdateProgressDialog
-{
-    private readonly Dialog _dialog;
-    private readonly ProgressBar _progressBar;
-    private readonly Label _infoLabel;
-    private readonly IApplication _app;
-
-    public UpdateProgressDialog(IApplication app, string newVersion)
-    {
-        _app = app;
-
-        _dialog = new Dialog { Title = $"Updating to {newVersion}", Width = 50, Height = 10 };
-
-        _infoLabel = new Label
-        {
-            Text = "Preparing update...",
-            X = 1,
-            Y = 1,
-            Width = Dim.Fill(2)
-        };
-
-        _progressBar = new ProgressBar
-        {
-            X = 1,
-            Y = 3,
-            Width = Dim.Fill(2),
-            Fraction = 0f
-        };
-
-        var cancelButton = new Button
-        {
-            Text = "Cancel",
-            X = Pos.Center(),
-            Y = 6
-        };
-
-        _dialog.Add(_infoLabel, _progressBar);
-    }
-
-    public void UpdateProgress(float fraction, string statusText)
-    {
-        _progressBar.Fraction = fraction;
-        _infoLabel.Text = statusText;
-    }
-
-    public void Show()
-    {
-        _app.Run(_dialog);
-    }
-
-    public void Close()
-    {
-        _app.RequestStop();
-    }
-}