feat(discord): enable session join leave buttons

Move neutral join/leave handlers into GmRelay.Shared so Telegram and Discord share capacity, waitlist, duplicate-click, and schedule-update behavior.

Add Discord component routing for join_session and leave_session buttons with deferred ephemeral replies and serialized schedule message updates.

Bump version to 2.5.0 and update Discord docs.

Refs #29

tests/GmRelay.Bot.Tests/Discord/DiscordPlatformMessengerTests.cs

@@ -7,9 +7,13 @@ namespace GmRelay.Bot.Tests.Discord;
 public sealed class DiscordPlatformMessengerTests
 {
     [Fact]
-    public void Constructor_ShouldAcceptRestClient()
+    public void Constructor_ShouldAcceptRestClientAndReplyCache()
     {
-        var constructor = typeof(DiscordPlatformMessenger).GetConstructor(new[] { typeof(NetCord.Rest.RestClient) });
+        var constructor = typeof(DiscordPlatformMessenger).GetConstructor(new[]
+        {
+            typeof(NetCord.Rest.RestClient),
+            typeof(DiscordInteractionReplyCache)
+        });
         Assert.NotNull(constructor);
     }
 
@@ -18,4 +22,30 @@ public sealed class DiscordPlatformMessengerTests
     {
         Assert.True(typeof(IPlatformMessenger).IsAssignableFrom(typeof(DiscordPlatformMessenger)));
     }
+
+    [Fact]
+    public async Task AnswerInteractionAsync_ShouldStoreReplyForComponentModule()
+    {
+        var source = await ReadRepositoryFileAsync("src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs");
+
+        Assert.Contains("DiscordInteractionReplyCache", source, StringComparison.Ordinal);
+        Assert.Contains("interactionReplies.Store(reply)", source, StringComparison.Ordinal);
+    }
+
+    private static async Task<string> ReadRepositoryFileAsync(string relativePath)
+    {
+        var directory = new DirectoryInfo(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            var candidate = Path.Combine(directory.FullName, relativePath);
+            if (File.Exists(candidate))
+            {
+                return await File.ReadAllTextAsync(candidate);
+            }
+
+            directory = directory.Parent;
+        }
+
+        throw new FileNotFoundException($"Could not locate repository file '{relativePath}'.");
+    }
 }