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.Web/Components/Layout/NavMenu.razor

@@ -73,7 +73,7 @@
                     </button>
                 </form>
 
-                <div class="nav-version">v3.0.4</div>
+                <div class="nav-version">v3.0.5</div>
             </div>
         </Authorized>
         <NotAuthorized>