feat(db): add feature flags schema for beta feature testing

Add feature_flags and feature_flag_access tables to support controlled
beta testing of new features in production without a separate test environment.

shared/db/schema/index.ts

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