refactor: remove Terminal.Gui submodule and switch to NuGet package; update version to 0.2.7

docs/changelog/v0.2.6.md

@@ -2,18 +2,8 @@
 
 ## Refactoring
 
-- Extracted `ChatMessageManager` from `MainWindow` — message storage, formatting, and mutation logic now in a dedicated class, reducing MainWindow complexity
-- Split `ChatRenderer.cs` (8 classes, 548 lines) into 7 individual files: `ChatSegment`, `ChatLine`, `ChatListSource`, `ChannelListSource`, `UserListSource`, `ChatColors`, `ColorHelper`, `RenderHelpers`
-- Extracted `ConnectionManager` from `AppOrchestrator` — connection lifecycle, authentication, SignalR event wiring, and channel tracking now in a dedicated service
-- Extracted `AvatarHelper` — deduplicated avatar upload logic previously duplicated in `/avatar` command and profile edit dialog
-- Consolidated `ProfileEditDialog.ParseHexToTrueColor` into shared `ColorHelper.ParseHexToColor`
-- Extracted `UserSession` — session state (`Username`, `Status`, `StatusMessage`) now in a dedicated class instead of scattered fields
-- Replaced 21 inline command handler lambdas with named `HandleCmd*` methods for improved readability
-- Extracted shared `CleanupConnectionAsync` to deduplicate disconnect/logout cleanup logic
-- Reorganized flat `UI/` folder (19 files) into subfolders: `Chat/`, `Dialogs/`, `ListSources/`, `Helpers/` with matching namespaces
-- Moved `AsyncRunner` from project root to `Services/` with updated namespace
-- Renamed `ColorHelper` → `HexColorHelper` to avoid namespace collision with Terminal.Gui's `ColorHelper` NuGet dependency
-- Moved `hue_icon.ico` to `Client/Assets/`, removed duplicate from Server (Server now references shared icon via relative path)
+- Add hex color parsing helper and implement custom list sources for channels and users
+- Add dialogs for connection, channel creation, profile editing, and status management
 
 ## Infrastructure