scripts/discover-*: four QoL upgrades from first live gap-analysis run

First real run surfaced 31 gap rows, ~20 of which were noise. These
changes reduce the output to actionable signal.

1. discover-unifi: /ea/devices now filters out
     - IPs outside the fleet LAN range (UDM's WAN IP appearing as a
       "device", ISP uplink records with public IPs)
     - UDM self-records (isConsole=true, or IP matches wans[].ipv4)
     - UCI records (UniFi Cable Internet = ISP modem tracking)
   LAN filter regex defaults to ^10\. (matches 10.0.0.0/8); override
   via UNIFI_LAN_FILTER env var if you run other private ranges.

2. discover-gaps: new --ignore-unifi flag drops rows where the final
   SOURCE column starts with "unifi:". Useful for "show me servery
   things to manage, not the fleet's network hardware."

3. discover-gaps: known-IP set now pulls IPs from
   servers/*/proxmox-details.txt AND servers/*/system-details.txt in
   addition to README.md and ssh-target. Consequence: VMs tracked by
   proxmox_inspect.sh are automatically counted as known without
   needing a separate servers/<vmname>/ dir. Also strips meaningless
   addresses (127.*, 0.0.0.0, 169.254.*) so they can't false-positive
   a "known" match.

4. MAC normalization: both discover-fortigate and discover-unifi now
   emit xx:xx:xx:xx:xx:xx lowercase. Previously FortiGate used colon
   format, UniFi used no-separator uppercase — same MAC looked
   different per source. Fortigate does tolower() in awk; UniFi uses
   a shared jq `norm_mac` function.

scripts/discover-fortigate.sh

@@ -100,7 +100,7 @@ awk -v src="fortigate:${HOST}" '
   # Lease row
   $1 ~ /^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$/ && $2 ~ /^[0-9a-fA-F]{2}:/ {
     ip   = $1
-    mac  = $2
+    mac  = tolower($2)   # normalize to lowercase — matches UniFi output
     host = (NF >= 3 && $3 !~ /^[0-9]+$/) ? $3 : "-"
     printf "%s\t%s\t%s\t%s\t%s\n", ip, mac, host, (iface==""?"-":iface), src
   }