Refactor OpenAPI fetcher for improved clarity and robustness

Reorganized and enhanced the OpenAPI fetch logic for better maintainability and error handling. Key updates include improved environment variable validation, more detailed error messages, streamlined configuration loading, and additional safety checks for file paths and directories. Added proper logging and ensured the process flow is easy to trace.

frontend/fetch-openapi.js

@@ -142,10 +142,18 @@ async function fetchAndGenerate() {
 }
 
 // Backend directory based on the environment
-const backendDirectory =
-    nodeEnv === 'test'
-        ? path.resolve('/home/jungfrau/heidi-v2/backend/app')
-        : path.resolve('/Users/gotthardg/PycharmProjects/heidi-v2/backend/app');
+// Backend directory based on the environment
+const backendDirectory = (() => {
+    switch (nodeEnv) {
+        case 'prod':
+            return path.resolve('/home/jungfrau/heidi-v2/backend/app'); // Production path
+        case 'test':
+            return path.resolve('/home/jungfrau/heidi-v2/backend/app'); // Test path
+        case 'dev':
+        default:
+            return path.resolve('/Users/gotthardg/PycharmProjects/heidi-v2/backend/app'); // Development path
+    }
+})();
 
 if (!fs.existsSync(backendDirectory)) {
     console.error(`❌ Backend directory does not exist: ${backendDirectory}`);