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`.

packages/shared/src/errors/index.ts

@@ -33,30 +33,6 @@ export class UnauthorizedError extends AppError {
   }
 }
 
-export class ForbiddenError extends AppError {
-  constructor(message = "Forbidden") {
-    super(message, "FORBIDDEN", 403);
-    this.name = "ForbiddenError";
-  }
-}
-
-export class ConflictError extends AppError {
-  constructor(message: string) {
-    super(message, "CONFLICT", 409);
-    this.name = "ConflictError";
-  }
-}
-
-export class InternalServerError extends AppError {
-  constructor(
-    message = "Internal server error",
-    details?: Record<string, unknown>,
-  ) {
-    super(message, "INTERNAL_SERVER_ERROR", 500, details);
-    this.name = "InternalServerError";
-  }
-}
-
 export class DatabaseError extends AppError {
   constructor(message: string, details?: Record<string, unknown>) {
     super(message, "DATABASE_ERROR", 500, details);
@@ -70,17 +46,3 @@ export class ConfigError extends AppError {
     this.name = "ConfigError";
   }
 }
-
-export class DiscordError extends AppError {
-  constructor(message: string, details?: Record<string, unknown>) {
-    super(message, "DISCORD_ERROR", 500, details);
-    this.name = "DiscordError";
-  }
-}
-
-export class TimeoutError extends AppError {
-  constructor(operation: string) {
-    super(`${operation} timed out`, "TIMEOUT", 504);
-    this.name = "TimeoutError";
-  }
-}