fix(discord): resolve slash commands from interaction payload instead of gateway cache

Context.Guild in NetCord resolves the Guild object from the gateway client cache
(cache.Guilds.GetValueOrDefault(guildId)), not from the interaction JSON payload.
After a bot restart, the guild may not yet be cached when the first slash command
arrives, causing Context.Guild to be null even though the command is invoked
inside a guild channel. This produced "This command can only be used in a guild."

Changes:
- DiscordListSessionsCommand: use Context.Interaction.GuildId instead of Context.Guild.Id
- DiscordNewSessionCommand: use Context.Interaction.GuildId + REST GetGuildAsync/GetGuildUserAsync
- DiscordRescheduleCommand: same as above
- DiscordSessionInteractionModule: same fix for button interactions (CreateInput)
- Add null guard in GetResolvedPermissions for safety
- Bump version to 3.0.5

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

src/GmRelay.DiscordBot/Features/Sessions/DiscordRescheduleCommand.cs

@@ -22,8 +22,10 @@ public class DiscordRescheduleCommand : ApplicationCommandModule<SlashCommandCon
         [SlashCommandParameter(Name = "option3", Description = "Third time option (optional)")] string? option3 = null,
         [SlashCommandParameter(Name = "deadline", Description = "Voting deadline (YYYY-MM-DD HH:mm)")] string deadline = "")
     {
-        var guild = Context.Guild
+        var guildId = Context.Interaction.GuildId
             ?? throw new InvalidOperationException("This command can only be used in a guild.");
+        var guild = await Context.Client.Rest.GetGuildAsync(guildId);
+        var member = await Context.Client.Rest.GetGuildUserAsync(guildId, Context.User.Id);
 
         if (!Guid.TryParse(sessionIdText, out var sessionId))
         {
@@ -64,7 +66,7 @@ public class DiscordRescheduleCommand : ApplicationCommandModule<SlashCommandCon
             return;
         }
 
-        var resolvedPermissions = GetResolvedPermissions(guild, Context.User.Id);
+        var resolvedPermissions = GetResolvedPermissions(guild, member);
 
         try
         {
@@ -102,12 +104,13 @@ public class DiscordRescheduleCommand : ApplicationCommandModule<SlashCommandCon
         }
     }
 
-    private static ulong GetResolvedPermissions(NetCord.Gateway.Guild guild, ulong userId)
+    private static ulong GetResolvedPermissions(NetCord.Rest.RestGuild guild, NetCord.GuildUser member)
     {
-        if (!guild.Users.TryGetValue(userId, out var guildUser))
+        if (member is null)
             return 0;
+
         ulong resolved = 0;
-        foreach (var roleId in guildUser.RoleIds)
+        foreach (var roleId in member.RoleIds)
         {
             if (guild.Roles.TryGetValue(roleId, out var role))
                 resolved |= (ulong)role.Permissions;