fix(network): derive the host IP from the default route, not hostname -I order

On a fresh ISO node, NetBird's own WireGuard tunnel (10.44.0.1) sorted
ahead of the real NIC in hostname -I, so the NetBird launch URL (and the
{{HOST_IP}} baked into its cert/config) pointed at the tunnel instead of
the LAN address. The main routing table's default route names the
physical uplink even while a VPN is active (NetBird/Tailscale steer
traffic via policy-routing rules, not the main table), so read src/dev
from 'ip -4 route show default' first, then fall back to a connected UDP
socket's source address, then to the old hostname -I scan.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/container/docker_packages.rs

@@ -696,22 +696,11 @@ async fn netbird_configured_launch_url() -> Option<String> {
     PodmanClient::lan_address_for("netbird")
 }
 
-/// First address from `hostname -I` — the node's primary host IP. Mirrors the
-/// orchestrator's `detect_host_ip` so launch URLs match the cert/config the
-/// orchestrator renders for `{{HOST_IP}}`.
+/// The node's primary host IP. Mirrors the orchestrator's `detect_host_ip`
+/// so launch URLs match the cert/config the orchestrator renders for
+/// `{{HOST_IP}}`.
 async fn first_host_ip() -> Option<String> {
-    let out = tokio::process::Command::new("hostname")
-        .arg("-I")
-        .output()
-        .await
-        .ok()?;
-    if !out.status.success() {
-        return None;
-    }
-    String::from_utf8_lossy(&out.stdout)
-        .split_whitespace()
-        .next()
-        .map(ToOwned::to_owned)
+    crate::host_ip::primary_host_ipv4().await
 }
 
 async fn reachable_lan_address(app_id: &str, candidate: Option<String>) -> Option<String> {