refactor: extract remaining Telegram handlers to platform-neutral contracts

- Extract CreateSessionHandler, ListSessionsHandler, DeleteSessionHandler,
  ExportCalendarHandler, HandleRescheduleTimeInputHandler,
  HandleRescheduleVoteHandler to GmRelay.Shared
- Add IPlatformMessenger methods: SendScheduleAsync, UpdateScheduleAsync,
  SendGroupMessageAsync with actions, CreateThreadAsync, DeleteThreadAsync
- Rewrite Telegram Bot wrappers as thin adapters delegating to shared handlers
- Rewrite DiscordRescheduleVoteHandler to use shared HandleRescheduleVoteHandler
- Update UpdateRouter with explicit type aliases for ambiguous handler names
- Add contract and source-inspection tests for extracted handlers
- Bump version 3.1.1 → 3.2.0

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/GmRelay.Bot.Tests/Features/Sessions/RescheduleSession/HandleRescheduleTimeInputHandlerTests.cs

@@ -1,4 +1,4 @@
-using GmRelay.Bot.Features.Sessions.RescheduleSession;
+using BotHandler = GmRelay.Bot.Features.Sessions.RescheduleSession.HandleRescheduleTimeInputHandler;
 using GmRelay.Shared.Features.Sessions.RescheduleSession;
 
 namespace GmRelay.Bot.Tests.Features.Sessions.RescheduleSession;
@@ -72,7 +72,7 @@ public sealed class HandleRescheduleTimeInputHandlerTests
             new(secondOptionId, bobId, "Bob", null)
         };
 
-        var text = HandleRescheduleTimeInputHandler.BuildVotingMessage(
+        var text = BotHandler.BuildVotingMessage(
             "Shadowrun",
             currentTime,
             deadline,
@@ -101,7 +101,7 @@ public sealed class HandleRescheduleTimeInputHandlerTests
             new(secondOptionId, 2, new DateTimeOffset(2026, 4, 27, 17, 0, 0, TimeSpan.Zero))
         };
 
-        var keyboard = HandleRescheduleTimeInputHandler.BuildVotingKeyboard(options);
+        var keyboard = BotHandler.BuildVotingKeyboard(options);
         var buttons = keyboard.InlineKeyboard.SelectMany(row => row).ToList();
 
         Assert.Collection(

tests/GmRelay.Bot.Tests/Features/Sessions/RescheduleSession/RescheduleCommandContractTests.cs

@@ -0,0 +1,43 @@
+using GmRelay.Shared.Features.Sessions.RescheduleSession;
+using GmRelay.Shared.Platform;
+
+namespace GmRelay.Bot.Tests.Features.Sessions.RescheduleSession;
+
+public sealed class RescheduleCommandContractTests
+{
+    [Fact]
+    public void HandleRescheduleTimeInputCommand_ShouldExposePlatformNeutralContext()
+    {
+        AssertProperty<HandleRescheduleTimeInputCommand>("User", typeof(PlatformUser));
+        AssertProperty<HandleRescheduleTimeInputCommand>("Group", typeof(PlatformGroup));
+        AssertProperty<HandleRescheduleTimeInputCommand>("Text", typeof(string));
+        AssertNoTelegramSpecificProperties<HandleRescheduleTimeInputCommand>();
+    }
+
+    [Fact]
+    public void HandleRescheduleVoteCommand_ShouldExposePlatformNeutralContext()
+    {
+        AssertProperty<HandleRescheduleVoteCommand>("OptionId", typeof(Guid));
+        AssertProperty<HandleRescheduleVoteCommand>("User", typeof(PlatformUser));
+        AssertProperty<HandleRescheduleVoteCommand>("Group", typeof(PlatformGroup));
+        AssertProperty<HandleRescheduleVoteCommand>("InteractionId", typeof(string));
+        AssertProperty<HandleRescheduleVoteCommand>("ScheduleMessage", typeof(PlatformMessageRef));
+        AssertNoTelegramSpecificProperties<HandleRescheduleVoteCommand>();
+    }
+
+    private static void AssertProperty<T>(string name, Type expectedType)
+    {
+        var property = Assert.Single(typeof(T).GetProperties(), p => p.Name == name);
+        Assert.Equal(expectedType, property.PropertyType);
+    }
+
+    private static void AssertNoTelegramSpecificProperties<T>()
+    {
+        var names = typeof(T).GetProperties().Select(p => p.Name).ToArray();
+        Assert.DoesNotContain(names, name => name.Contains("Telegram", StringComparison.Ordinal));
+        Assert.DoesNotContain("ChatId", names);
+        Assert.DoesNotContain("MessageId", names);
+        Assert.DoesNotContain("TelegramUserId", names);
+        Assert.DoesNotContain("TelegramUsername", names);
+    }
+}