Add a Rocky Linux 9 virtual machine

run-rocky9.py with its QEMU config, port forwards (SSH on 2226) and
cloud-init seed, modelled on the Fedora 44 launcher. Update vm-images for
the rocky9 download target.

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

seediso/README.md

@@ -7,6 +7,7 @@ Each operating system has an independent NoCloud configuration and generated
 seediso/
 ├── debian13/
 ├── almalinux10/
+├── rocky9/
 ├── fedora44/
 └── ubuntu2604/
 ```