The create form accepts zero or negative vCPUs and memory #175

Found in the frontend review of #172.

NewVMForm (built on the CreateInstance model) has no minimum for vcpu, memory or hdd_size. The page posts with formnovalidate, so the browser does not enforce its own min=1 either. A value of 0 or below passes form validation and only fails later in libvirt, inside the job.

The MAC pattern on the page also accepts incomplete addresses such as aa:.

Suggested fix:

• Validate positive values in the form.
• Check the MACs there with the existing helper (utils.nic_macs), so the user gets an error on the field instead of a failed job.