feat: implement Blazor web interface for GM session management

- Created GmRelay.Web project (Blazor Server)
- Created GmRelay.Shared library for domain models and rendering
- Refactored GmRelay.Bot to use the Shared library
- Integrated Telegram Login widget with server-side HMAC verification
- Added Dashboard, Group Details, and Edit Session pages
- Enabled bot notifications and in-place message updates from web actions
- Updated .NET Aspire orchestration and Docker Compose configuration

src/GmRelay.Shared/Domain/SessionStatus.cs

@@ -0,0 +1,9 @@
+namespace GmRelay.Shared.Domain;
+
+public static class SessionStatus
+{
+    public const string Planned = "Planned";
+    public const string ConfirmationSent = "ConfirmationSent";
+    public const string Confirmed = "Confirmed";
+    public const string Cancelled = "Cancelled";
+}