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/package.json

@@ -7,7 +7,7 @@
   "types": "dist/index.d.ts",
   "exports": {
     ".": "./dist/index.js",
-    "./types": "./dist/types/index.js",
+    "./config": "./dist/config/index.js",
     "./errors": "./dist/errors/index.js",
     "./logger": "./dist/logger/index.js",
     "./utils": "./dist/utils/index.js"