feat(db): add guild_settings table for per-guild configuration

Store guild-specific settings (roles, channels, moderation options) in
database instead of config file, enabling per-guild configuration and
runtime updates without redeployment.

shared/db/schema/index.ts

@@ -5,3 +5,4 @@ export * from './economy';
 export * from './quests';
 export * from './moderation';
 export * from './feature-flags';
+export * from './guild-settings';