refactor: remove unused Caddy configuration and validation code

- Deleted Caddy configuration types and validation logic from the backend.
- Removed associated test files for validation.
- Cleaned up related service and model files that are no longer needed.
- Removed unnecessary environment configuration and database connection code.
- Eliminated unused models related to access control, SSL certificates, and user management.
- Cleaned up node modules by removing unnecessary binaries.

backend/node_modules/.bin/parser

@@ -1 +0,0 @@
-../@babel/parser/bin/babel-parser.js