v0.2.5 - Audio Playback, File Downloads & IRC Fixes

Features

New Audio message type — uploaded audio files (.mp3, .wav, .ogg, .flac, .aac, .m4a, .wma) are automatically detected and categorized
TUI client renders audio messages with ♪ [Audio: filename] (Enter to play) indicator
Press Enter on an audio message to play it locally via AudioPlaybackService (NetCoreAudio)
IRC gateway formats audio messages as ♪ [Audio: filename] url
Server detects audio files by extension via FileValidationHelper.IsAudioFile()

Press Enter on a file message in the TUI client to download it to the local machine
ApiClient.DownloadFileAsync() streams file downloads from the server
File and audio messages in the chat list now show colored indicators with interaction hints

FileCleanupService (BackgroundService) periodically removes old uploaded files
Configurable via Storage:CleanupIntervalHours (default 1h) and Storage:RetentionDays (default 30d)

DataMigrationService runs at startup to handle schema/data evolution
Ensures #general channel and pre-existing channels are marked public
Migrates legacy ANSI escape codes in image messages to printable color tags ({F:RRGGBB}, {B:RRGGBB}, {X})
Migrates legacy single-object EmbedJson to array format
Promotes usernames listed in Server:Admins config to Admin role

Fixed: IRC JOIN history replay showed encrypted gibberish — IrcCommandHandler.HandleJoinAsync now decrypts channel history before formatting for IRC clients (history was encrypted for SignalR transport but sent raw to IRC)
Fixed: JoinedChannels race condition — IrcClientConnection.JoinedChannels replaced with thread-safe methods (JoinChannel, LeaveChannel, IsInChannel, GetJoinedChannels) using lock synchronization; prevents crashes when broadcaster threads read while the command handler writes
Fixed: RequireRegistered fire-and-forget — converted from sync bool to async Task<bool> (RequireRegisteredAsync) so the error reply is properly awaited before the handler returns

Audio MIME types in FilesController (mp3, wav, ogg, flac, aac, m4a, wma)
Test suites: ChatLine, CommandHandler, DataMigrationService, FileValidationHelper, ImageToAsciiService, IrcMessageFormatter, JwtTokenService, LinkEmbedService
IRC abstraction layer test suite: IrcMessage parsing, IrcMessageFormatter, IrcClientConnection, IrcCommandHandler, IrcBroadcaster
Test helpers: TestDuplexStream, TestIrcConnectionFactory, FakeChatService, FakeEncryptionService for IRC unit testing without network I/O
214 total tests