refactor(shared): centralize configuration and types

Migrate configuration validation and core moderation types from individual services to the `@bete/shared` package to ensure consistency across the monorepo.

- Move `AppConfig` and moderation-related interfaces to `packages/shared`.
- Replace service-specific Zod schemas with the centralized shared configuration.
- Refactor `services/backend` and `services/discord-gateway` to consume shared config and types.
- Remove redundant type definitions and local configuration logic in services.
- Update `packages/shared` exports to include new `config` and `moderation-types` modules.
- Clean up unused files and deprecated utility functions in `packages/shared`.

services/backend/src/ws/redis-bridge.ts

@@ -32,14 +32,7 @@ const SUBSCRIPTIONS: ChannelMapping[] = [
 let subscriber: Redis | null = null;
 
 function createSubscriber(): Redis {
-  if (config.REDIS_URL) {
-    return new Redis(config.REDIS_URL, { keyPrefix: "" });
-  }
-  return new Redis({
-    host: config.REDIS_HOST,
-    port: config.REDIS_PORT,
-    keyPrefix: "",
-  });
+  return new Redis(config.REDIS_URL, { keyPrefix: "" });
 }
 
 /**
@@ -93,7 +86,7 @@ function handleSubscriptionMessage(channel: string, message: string): void {
 }
 
 export async function startRedisBridge(): Promise<void> {
-  if (!config.REDIS_URL && !config.REDIS_HOST) {
+  if (!config.REDIS_URL) {
     logger.info("Redis not configured, skipping Redis bridge");
     return;
   }