Configure Playwright for headless CI and add Gitea workflow with container support

backend/app/server.js

@@ -132,6 +132,10 @@ app.get('/api/health', (req, res) => {
   res.json({ status: 'ok', timestamp: new Date().toISOString() });
 });
 
-app.listen(PORT, '0.0.0.0', () => {
-  console.log(`Line of Sight Backend running on port ${PORT}`);
-});
+if (require.main === module) {
+  app.listen(PORT, '0.0.0.0', () => {
+    console.log(`Line of Sight Backend running on port ${PORT}`);
+  });
+}
+
+module.exports = { app, calculateDestination };