For DHCP setups DNS is delivered with the lease, but with a static IP the
container inherits /etc/resolv.conf from the PVE host - which is often
unreachable from the container's VLAN.
Changes:
- New NAMESERVER prompt (only shown for static IPs, defaults to gateway)
- pct create now passes --nameserver when set
- Network wait loop tests L3 and DNS separately so failures point at the
actual cause (no route to gateway vs. bad DNS server)
- Refactored pct create args into an array for cleaner conditional flags