feat: add centralized error logging system

- Implemented Error Log API to capture and store error logs from various services.
- Updated admin_ui to include Error Log Viewer component for inspecting logs.
- Enhanced error handling in auth_api, employee_api, and transit_api to report errors to the Error Log API.
- Modified existing services to utilize the new error logging functionality.
- Updated Docker Compose configuration to include the Error Log API service.
- Added error logging service in bus_terminal for Flutter application.

employee_api/index.js

@@ -6,6 +6,44 @@ require('dotenv').config();
 const app = express();
 app.use(express.json());
 
+const ERROR_LOG_API_URL = process.env.ERROR_LOG_API_URL || 'http://localhost:5003/error_log';
+
+function friendlyErrorMessage(statusCode) {
+    if (statusCode === 400) return 'Controleer je invoer en probeer opnieuw.';
+    if (statusCode === 401) return 'Je sessie is verlopen. Log opnieuw in.';
+    if (statusCode === 403) return 'Je hebt hier geen toegang toe.';
+    if (statusCode === 404) return 'Niet gevonden.';
+    return 'Er ging iets mis. Probeer het later opnieuw.';
+}
+
+async function reportError({ partOfService, error }) {
+    try {
+        await fetch(ERROR_LOG_API_URL, {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({
+                service: 'employee_api',
+                partOfService,
+                error,
+            }),
+        });
+    } catch (_) {}
+}
+
+app.use((req, res, next) => {
+    const originalJson = res.json.bind(res);
+    res.json = (body) => {
+        if (res.statusCode >= 400 && body && typeof body === 'object') {
+            const rawError = body.error || body.message || body.details || `HTTP ${res.statusCode}`;
+            void reportError({ partOfService: `${req.method} ${req.originalUrl}`, error: rawError });
+            return originalJson({ error: friendlyErrorMessage(res.statusCode) });
+        }
+        return originalJson(body);
+    };
+
+    next();
+});
+
 // Employee onboarding
 app.post('/createemployee', async (req, res) => {
     try {
@@ -20,8 +58,9 @@ app.post('/createemployee', async (req, res) => {
         return res.status(201).json({ employee: firstname, code: newUser.usercoden });
     }
     catch (err) {
-    console.error(err);
-    res.status(500).json({ error: 'internal_error' });
+        void reportError({ partOfService: `${req.method} ${req.originalUrl}`, error: err?.stack || err?.message || String(err) });
+        console.error(err);
+        res.status(500).json({ error: friendlyErrorMessage(500) });
   }
 })
 
@@ -30,8 +69,9 @@ app.get('/health', async (_req, res, _next) => {
     return res.status(200).json({endpoint: 'reachable'})
     }
     catch (err) {
+        void reportError({ partOfService: `${req.method} ${req.originalUrl}`, error: err?.stack || err?.message || String(err) });
         console.error(err);
-        res.status(500).json({endpoint: 'unreachable'})
+        res.status(500).json({ endpoint: 'unreachable', error: friendlyErrorMessage(500) })
     }
 })