feat: Update database connection and error display settings

- Changed database connection credentials in footer.php for improved security.
- Disabled error display in ajax.inc.php to prevent sensitive information exposure.
- Added comprehensive design documentation for the news flow application.
- Implemented a modernized index.php layout with responsive design and enhanced user experience.
- Developed main.js for dynamic news loading, including infinite scroll and date filtering functionalities.
- Structured interaction.md to detail core interactive features of the application.
- Organized outline.md to clarify project structure and core functionalities.
- Populated mock-data.json with realistic news data for testing and development purposes.

html/footer.php

@@ -13,7 +13,7 @@
 <span style='color:grey;font-size:small;'>
 <?php
 ini_set("display_errors", "1");
-$mysqli = new mysqli('localhost','root','nancysimon','myquant');
+$mysqli = new mysqli('localhost','myquant','_H(lU1_fF*9baRTp','myquant');
 function log_pv(){
     #echo "start log";
     global $mysqli;