Enhance API documentation and restructure routes for improved clarity

- Updated README.md to include comprehensive Swagger documentation details, highlighting new features and endpoint categories.
- Introduced a new router structure to streamline route registration for admin and public endpoints, enhancing maintainability.
- Updated health check endpoint documentation to reflect comprehensive server status information.
- Enhanced customer and company management routes with improved descriptions and examples in Swagger.
- Refactored customer and user handlers to remove obsolete route registrations, aligning with the new router structure.
- Improved response handling in customer and user services to utilize string IDs consistently.
- Updated validation rules and forms for customer management to support multiple company assignments.
- Enhanced logging practices across services to ensure better traceability and error handling.

pkg/logger/LOGGING_UPGRADE.md

@@ -56,7 +56,7 @@ The logger interface remains the same - **no code changes required** in existing
 ```go
 // All existing code continues to work
 log.Info("User logged in", map[string]interface{}{
-    "user_id": user.ID.String(),
+    "user_id": user.ID.Hex(),
     "email":   user.Email,
 })