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/internal/database/database.go

@@ -1,18 +0,0 @@
-package database
-
-import (
-	"fmt"
-
-	"gorm.io/driver/sqlite"
-	"gorm.io/gorm"
-)
-
-// Connect opens a SQLite database connection.
-func Connect(dbPath string) (*gorm.DB, error) {
-	db, err := gorm.Open(sqlite.Open(dbPath), &gorm.Config{})
-	if err != nil {
-		return nil, fmt.Errorf("open database: %w", err)
-	}
-
-	return db, nil
-}