SSDP multicast (239.255.255.250:2021) doesn't traverse routers, so a
printer behind a router on a different L3 segment was invisible to
"Discover Printers on Network". Docker mode had a CIDR text input but
only as a fallback when zero interface subnets were detected; native
mode had no subnet field at all.
AddPrinterModal now surfaces an always-visible subnet picker. Detected
interface subnets stay as dropdown options, plus a "Custom subnet..."
sentinel reveals a CIDR text input. When custom is picked, discovery
routes through POST /discovery/scan with the typed CIDR instead of
SSDP (which would no-op against a foreign subnet anyway). Last custom
CIDR persisted to localStorage so VLAN users don't retype every time.
Scan button label and scanning / no-printers-found strings all key off
(isDocker || useCustomSubnet) so wording stays "Scan Subnet..." /
"Scanning subnet..." whether the user is on Docker or just picked
Custom.
Backend unchanged: SubnetScanner.scan_subnet() already accepts any
CIDR, already caps at /22 (1024 hosts), POST /discovery/scan already
takes user-supplied input.
maziggy
eb418a5b37