chore: update .gitignore to exclude backup and downloaded files

- Add *.bak pattern for backup files
- Add *.old pattern for old file versions
- Add *.backup pattern for backup files
- Add *.squashfs* pattern for squashfs images
- Add vmlinux-* pattern for kernel files

Author: restuhaqza

.gitignore

@@ -178,3 +178,12 @@ ssh_keys/
 
 # Generated/downloaded Firecracker files (kernel, rootfs images)
 firecracker-files/
+
+# Backup files
+*.bak
+*.old
+*.backup
+
+# Large downloaded files in project root
+*.squashfs*
+vmlinux-*