fix(discord): allow all channels when no channel allowlist is configured

When a guild is in the allowlist but has no channels configured,
all channels should be allowed. Previously, an empty channels object
({}) would cause channelConfig to return {allowed: false}, blocking
all messages.

Now the code checks for both null/undefined AND empty object,
returning null in both cases which results in channelAllowed=true.

src/discord/monitor/allow-list.ts

@@ -258,7 +258,8 @@ export function resolveDiscordChannelConfigWithFallback(params: {
     scope,
   } = params;
   const channels = guildInfo?.channels;
-  if (!channels) return null;
+  // Return null if channels is undefined, null, or empty object - allows all channels when no allowlist is configured
+  if (!channels || Object.keys(channels).length === 0) return null;
   const resolvedParentSlug = parentSlug ?? (parentName ? normalizeDiscordSlug(parentName) : "");
   const match = resolveDiscordChannelEntryMatch(
     channels,