feat: Implement end-to-end encryption for channels

- Added EncryptionSalt and WrappedRoomKey properties to Channel model.
- Introduced RoomCrypto class for client-side encryption and decryption.
- Updated ChannelService to handle encrypted channels, including creation and rekeying.
- Modified ChannelsController to expose crypto metadata and rekey functionality.
- Enhanced IrcCommandHandler to block joining encrypted channels over IRC.
- Updated database schema with migration for new encryption fields.
- Refactored file validation and image processing services to accommodate encrypted channels.
- Added unit tests for RoomCrypto functionality and updated existing tests for channel services.

src/EchoHub.Tests/Irc/IrcCommandHandlerTests.cs

@@ -287,6 +287,17 @@ public class IrcCommandHandlerTests
         Assert.Contains(lines, l => l.Contains("475") && l.Contains("#secret") && l.Contains("+k"));
     }
 
+    [Fact]
+    public async Task Join_EncryptedChannel_IsBlockedOverIrc()
+    {
+        _channelService.CryptoToReturn = new ChannelCryptoDto(true, "c2FsdA==");
+
+        var lines = await RunAuthenticated(["JOIN #vault"]);
+
+        Assert.Contains(lines, l => l.Contains("475") && l.Contains("#vault") && l.Contains("end-to-end encrypted"));
+        Assert.Empty(_chatService.JoinedChannels);
+    }
+
     [Fact]
     public async Task Join_SendsTopic()
     {