feat: improve error handling and logging in the web application

- Updated the error handling in `index.html` to include a retry button for failed app loads, enhancing user experience.
- Added session storage management to prevent repeated reloads on errors.
- Enhanced the `.gitignore` file to include log files, improving project cleanliness.
- Included error logging in `main.js` to ensure better tracking of issues during app initialization.

webapp/js/main.js

@@ -68,6 +68,9 @@ applyLangToUi();
 
 logger.info("App init", "lang=" + state.lang);
 
+try {
+  sessionStorage.removeItem("__dtLoadRetry");
+} catch (_) {}
 window.__dtReady = true;
 
 /**