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.Tests/CommandHandlerTests.cs

@@ -472,4 +472,22 @@ public class CommandHandlerTests
         Assert.True(result.Handled);
         Assert.True(quitCalled);
     }
+
+    // ── /meta ─────────────────────────────────────────────────────────
+
+    [Theory]
+    [InlineData("/meta")]
+    [InlineData("/info")]
+    public async Task HandleAsync_Meta_RaisesRoomInfo(string input)
+    {
+        var handler = CreateHandler();
+        var raised = false;
+        handler.OnRoomInfo += () => { raised = true; return Task.CompletedTask; };
+
+        var result = await handler.HandleAsync(input);
+
+        Assert.True(result.Handled);
+        Assert.False(result.IsError);
+        Assert.True(raised);
+    }
 }

src/EchoHub.Tests/Irc/TestHelpers.cs

@@ -270,6 +270,11 @@ internal sealed class FakeChannelService : IChannelService
     public Task<ChannelDto?> GetChannelByNameAsync(string channelName) =>
         Task.FromResult(ChannelByNameToReturn);
 
+    public ChannelMetaDto? ChannelMetaToReturn { get; set; }
+
+    public Task<ChannelMetaDto?> GetChannelMetaAsync(string channelName) =>
+        Task.FromResult(ChannelMetaToReturn);
+
     public Task<(bool Success, string? Error, bool PasswordRequired)> EnsureChannelMembershipAsync(Guid userId, string channelName, string? password = null) =>
         Task.FromResult(MembershipResult);
 }

src/EchoHub.Tests/UploadLimitsTests.cs

@@ -0,0 +1,66 @@
+using EchoHub.Core.Constants;
+using EchoHub.Core.Models;
+using EchoHub.Server.Config;
+using Microsoft.Extensions.Configuration;
+using Xunit;
+
+namespace EchoHub.Tests;
+
+public class UploadLimitsTests
+{
+    [Fact]
+    public void Defaults_MirrorHubConstants()
+    {
+        var limits = new UploadLimits();
+
+        Assert.Equal(HubConstants.MaxFileSizeBytes, limits.MaxFileSizeBytes);
+        Assert.Equal(HubConstants.MaxImageSizeBytes, limits.MaxImageSizeBytes);
+        Assert.Equal(HubConstants.MaxAudioFileSizeBytes, limits.MaxAudioSizeBytes);
+        Assert.Equal(HubConstants.MaxAvatarSizeBytes, limits.MaxAvatarSizeBytes);
+        Assert.Equal(HubConstants.MaxAttachmentsPerMessage, limits.MaxAttachmentsPerMessage);
+    }
+
+    [Fact]
+    public void MaxForKind_MapsEachAttachmentKind()
+    {
+        var limits = new UploadLimits
+        {
+            MaxImageSizeMB = 5,
+            MaxAudioSizeMB = 7,
+            MaxFileSizeMB = 11,
+        };
+
+        Assert.Equal(5L * 1024 * 1024, limits.MaxForKind(AttachmentKind.Image));
+        Assert.Equal(7L * 1024 * 1024, limits.MaxForKind(AttachmentKind.Audio));
+        Assert.Equal(11L * 1024 * 1024, limits.MaxForKind(AttachmentKind.File));
+    }
+
+    [Fact]
+    public void MaxRequestBodyBytes_IsFileSizeTimesAttachmentCap()
+    {
+        var limits = new UploadLimits { MaxFileSizeMB = 20, MaxAttachmentsPerMessage = 4 };
+
+        Assert.Equal(20L * 1024 * 1024 * 4, limits.MaxRequestBodyBytes);
+    }
+
+    [Fact]
+    public void BoundFromConfiguration_OverridesDefaults()
+    {
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["Uploads:MaxFileSizeMB"] = "250",
+                ["Uploads:MaxImageSizeMB"] = "25",
+                ["Uploads:MaxAttachmentsPerMessage"] = "3",
+            })
+            .Build();
+
+        var limits = config.GetSection("Uploads").Get<UploadLimits>()!;
+
+        Assert.Equal(250L * 1024 * 1024, limits.MaxFileSizeBytes);
+        Assert.Equal(25L * 1024 * 1024, limits.MaxImageSizeBytes);
+        Assert.Equal(3, limits.MaxAttachmentsPerMessage);
+        // Unspecified values keep their HubConstants-derived defaults.
+        Assert.Equal(HubConstants.MaxAudioFileSizeBytes, limits.MaxAudioSizeBytes);
+    }
+}