fix(build): rename HOSTNAME -> CT_HOSTNAME (shadowed bash builtin), add VLAN_TAG prompt, fail fast on network timeout

HOSTNAME is a bash built-in always containing the host's name, so the
"-z HOSTNAME" check never fired and the prompt was silently skipped —
containers ended up named after the Proxmox host.

Also added an optional VLAN tag prompt (empty = no tag), and the network
wait loop now exits with an error if the network never comes up instead
of silently proceeding to a guaranteed-broken apt-get update.

lib/build.func

@@ -11,6 +11,9 @@
 # and may override the DEFAULT_* values below.
 #
 # Caller may define print_app_summary() to customize the trailing summary.
+#
+# NB: We use CT_HOSTNAME (not HOSTNAME) because HOSTNAME is a bash built-in
+# that always holds the current host's name, which would defeat any prompt.
 
 # ── colors / logging ─────────────────────────────────────────────────────────
 if [[ -z "${_COLORS_LOADED:-}" ]]; then
@@ -61,6 +64,8 @@ show_header() {
 
 # ── prompts ──────────────────────────────────────────────────────────────────
 # Each prompt is skipped if the corresponding variable is already set in env.
+# VLAN_TAG uses ${VLAN_TAG+x} so that explicitly setting it to "" via env
+# skips the prompt (= "no VLAN, don't ask").
 prompt_lxc_config() {
   if [[ -z "${CTID:-}" ]]; then
     read -rp "Container ID [auto]: " CTID
@@ -68,9 +73,9 @@ prompt_lxc_config() {
   fi
   echo "  → CTID: $CTID"
 
-  if [[ -z "${HOSTNAME:-}" ]]; then
+  if [[ -z "${CT_HOSTNAME:-}" ]]; then
-    read -rp "Hostname [$DEFAULT_HOSTNAME]: " HOSTNAME
+    read -rp "Hostname [$DEFAULT_HOSTNAME]: " CT_HOSTNAME
-    HOSTNAME="${HOSTNAME:-$DEFAULT_HOSTNAME}"
+    CT_HOSTNAME="${CT_HOSTNAME:-$DEFAULT_HOSTNAME}"
   fi
   if [[ -z "${DISK_SIZE:-}" ]]; then
     read -rp "Disk size in GB [$DEFAULT_DISK]: " DISK_SIZE
@@ -88,6 +93,9 @@ prompt_lxc_config() {
     read -rp "Bridge [$DEFAULT_BRIDGE]: " BRIDGE
     BRIDGE="${BRIDGE:-$DEFAULT_BRIDGE}"
   fi
+  if [[ -z "${VLAN_TAG+x}" ]]; then
+    read -rp "VLAN tag (empty for none): " VLAN_TAG
+  fi
   if [[ -z "${TEMPLATE_STORAGE:-}" ]]; then
     read -rp "Template storage [$DEFAULT_TEMPLATE_STORAGE]: " TEMPLATE_STORAGE
     TEMPLATE_STORAGE="${TEMPLATE_STORAGE:-$DEFAULT_TEMPLATE_STORAGE}"
@@ -127,15 +135,17 @@ create_lxc() {
   ROOT_PASSWORD=$(openssl rand -base64 18)
 
   local net_opts="name=eth0,bridge=$BRIDGE"
+  [[ -n "${VLAN_TAG:-}" ]] && net_opts+=",tag=$VLAN_TAG"
   if [[ "$IPCFG" == "dhcp" ]]; then
     net_opts+=",ip=dhcp"
   else
     net_opts+=",ip=$IPCFG,gw=$GATEWAY"
   fi
 
-  msg_info "Creating unprivileged LXC $CTID ($HOSTNAME)..."
+  msg_info "Creating unprivileged LXC $CTID ($CT_HOSTNAME)..."
+  msg_info "  net0: $net_opts"
   pct create "$CTID" "$TEMPLATE_STORAGE:vztmpl/$TEMPLATE" \
-    --hostname "$HOSTNAME" \
+    --hostname "$CT_HOSTNAME" \
     --cores "$CORES" \
     --memory "$RAM" \
     --swap 512 \
@@ -156,11 +166,13 @@ create_lxc() {
   local i
   for i in {1..30}; do
     if pct exec "$CTID" -- getent hosts deb.debian.org >/dev/null 2>&1; then
-      break
+      msg_ok "Network up"
+      return 0
     fi
     sleep 2
   done
-  msg_ok "Network up"
+  msg_err "Network never came up. Check bridge/VLAN/gateway settings."
+  exit 1
 }
 
 # ── bootstrap installer inside the container ─────────────────────────────────
@@ -189,7 +201,7 @@ print_summary() {
   msg_ok "Installation complete!"
   echo
   echo "─────────────────────────────────────────────────────────────"
-  echo "  $APP LXC #$CTID — $HOSTNAME"
+  echo "  $APP LXC #$CTID — $CT_HOSTNAME"
   echo "─────────────────────────────────────────────────────────────"
   print_app_summary
   echo