Fix quick-register broadcast detection on Proxmox bridges

Two bugs compounded on Proxmox hosts: primary_iface walked
`ip link show` and picked the physical NIC (e.g. enp1s0), which has
no IPv4 on Proxmox because the address lives on vmbr0. Even if vmbr0
had been picked, the kernel reports its broadcast as 0.0.0.0, so the
script fell all the way back to 255.255.255.255.

Now we prefer the default-route interface (vmbr0 on Proxmox, eno1 on
bare metal) and, when `ip` doesn't surface a usable `brd`, compute
the broadcast from the inet CIDR instead of giving up.

internal/web/register/quick.sh.tmpl

@@ -26,16 +26,40 @@ if [[ -z "${ORCH_URL}" ]]; then
 fi
 
 primary_iface() {
-    # Pick the first physical ethernet-style interface that isn't a loopback,
-    # bridge, veth, docker, virbr, bond, tun, or tap.
-    ip -o link show 2>/dev/null \
-        | awk '$0 ~ /link\/ether/ {
-                 name=$2; sub(":","",name)
-                 if (name ~ /^(lo|docker|br-|veth|virbr|bond|tun|tap|wlan|wlp)/) next
+    # Prefer the interface carrying the default route — that's the
+    # canonical "primary" iface (e.g. vmbr0 on Proxmox, eno1 on bare
+    # metal). `ip link show` order picks the physical NIC on Proxmox,
+    # but that NIC has no IPv4, so we'd miss the broadcast address.
+    local iface
+    iface="$(ip -o -4 route show default 2>/dev/null \
+        | awk '{for(i=1;i<=NF;i++) if($i=="dev") {print $(i+1); exit}}')"
+    if [[ -n "${iface}" ]]; then
+        echo "${iface}"
+        return
+    fi
+    # Fallback: first non-virtual interface that has an IPv4 address.
+    ip -o -4 addr show 2>/dev/null \
+        | awk '{
+                 name=$2
+                 if (name ~ /^(lo|docker|br-|veth|virbr|bond|tun|tap|fwbr|fwpr|fwln|wlan|wlp)/) next
                  print name; exit
                }'
 }
 
+# compute_broadcast "192.168.1.250/24" → "192.168.1.255"
+compute_broadcast() {
+    local cidr="$1" ip prefix a b c d host mask inv bc
+    ip="${cidr%/*}"
+    prefix="${cidr#*/}"
+    [[ "${ip}" == *.*.*.* && "${prefix}" =~ ^[0-9]+$ ]] || return 1
+    IFS=. read -r a b c d <<<"${ip}"
+    host=$(( (a<<24) | (b<<16) | (c<<8) | d ))
+    mask=$(( (0xFFFFFFFF << (32 - prefix)) & 0xFFFFFFFF ))
+    inv=$(( (~mask) & 0xFFFFFFFF ))
+    bc=$(( host | inv ))
+    printf '%d.%d.%d.%d' $(( (bc>>24)&0xFF )) $(( (bc>>16)&0xFF )) $(( (bc>>8)&0xFF )) $(( bc&0xFF ))
+}
+
 IFACE="$(primary_iface || true)"
 if [[ -z "${IFACE}" ]]; then
     echo "ERROR: could not pick a primary network interface." >&2
@@ -50,8 +74,17 @@ if [[ -z "${MAC}" ]]; then
 fi
 
 if [[ -z "${WOL_BROADCAST:-}" ]]; then
-    WOL_BROADCAST="$(ip -o -4 addr show dev "${IFACE}" 2>/dev/null \
-        | awk '{for(i=1;i<=NF;i++) if($i=="brd") {print $(i+1); exit}}')"
+    ipinfo="$(ip -o -4 addr show dev "${IFACE}" 2>/dev/null || true)"
+    WOL_BROADCAST="$(awk '{for(i=1;i<=NF;i++) if($i=="brd") {print $(i+1); exit}}' <<<"${ipinfo}")"
+    # Bridges (vmbr0 on Proxmox, br0 on Linux bridges) often report
+    # brd 0.0.0.0 or omit it entirely. Compute from the inet CIDR
+    # before giving up on 255.255.255.255.
+    if [[ -z "${WOL_BROADCAST}" || "${WOL_BROADCAST}" == "0.0.0.0" ]]; then
+        cidr="$(awk '{for(i=1;i<=NF;i++) if($i=="inet") {print $(i+1); exit}}' <<<"${ipinfo}")"
+        if [[ "${cidr}" == */* ]]; then
+            WOL_BROADCAST="$(compute_broadcast "${cidr}" || true)"
+        fi
+    fi
 fi
 WOL_BROADCAST="${WOL_BROADCAST:-255.255.255.255}"
 WOL_PORT="${WOL_PORT:-9}"