Add database connection helper and live now-playing page

- includes/db.php: getDB() returns a shared PDO connection to MariaDB
- config/db_credentials.example.php: credentials template; the real
  db_credentials.php is gitignored and deployed separately via SFTP
- live.php: page for active broadcasts, with the player on the left
  and a placeholder Recently Played table on the right

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -28,3 +28,6 @@ Temporary Items
 # Don't commit the code-workspace files
 *.code-workspace
 
+
+# Database credentials — keep out of version control
+config/db_credentials.php