Read port forwards from per-VM forwards.conf files

A QEMU config file section cannot hold more than one hostfwd entry, so
the forwards move out of the ini files into qemu/<vm>/forwards.conf, one
"LABEL HOST_PORT GUEST_PORT" rule per line. The new vmforwards.py parses
them, skips rules whose host port is taken and builds the -netdev
argument, which every launcher now passes instead of relying on a
netdev section in the ini or on -nic.

The ini files move to qemu/<vm>/config.ini and qemu/<vm>/<os>-<arch>.ini.
The *_SSH_PORT / *_RDP_PORT variables and --rdp-port / --ssh-port still
replace the host port of the SSH and RDP rules.

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

qemu/debian13/forwards.conf

@@ -0,0 +1,2 @@
+# Host ports forwarded to the guest: LABEL HOST_PORT GUEST_PORT
+SSH  2222  22