fix(install): install Node 20 on Linux; Vite needs it

Debian apt ships EOL Node 18 which crashes Vite 8. Prep stage installs Node 20
from NodeSource when node is missing or <20; package.json declares engines.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bin/restore-linux.sh

@@ -35,8 +35,19 @@ if [ "$stage" = "prep" ]; then
         echo "Installing system packages..."
         sudo apt-get install -y --no-install-recommends \
             git sqlite3 curl python3-venv python3-gi gir1.2-gtk-3.0 \
-            nodejs npm xfce4-genmon-plugin plank blueman \
+            xfce4-genmon-plugin plank blueman \
             || echo "Warning: some system packages failed — install them manually."
+
+        # Node.js 20+: Vite needs 20.19+, but Debian/Ubuntu apt ship an EOL Node 18
+        # (its 'nodejs' package) which crashes Vite with 'CustomEvent is not defined'.
+        # Install from NodeSource only when the current node is missing or too old.
+        node_major=$(node -v 2>/dev/null | sed -E 's/^v([0-9]+).*/\1/')
+        if [ -z "$node_major" ] || [ "$node_major" -lt 20 ]; then
+            echo "Installing Node.js 20 (found: ${node_major:-none})..."
+            curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash - \
+                && sudo apt-get install -y nodejs \
+                || echo "Warning: Node 20 install failed — install Node 20+ manually (Vite needs it)."
+        fi
     fi
     exit 0
 fi