Add 4GB swap file on root filesystem to prevent OOM kills

Homepage request causes PHP-FPM to spike to ~400MB, exhausting all
available memory (985MB total, ~400MB free at idle). Without swap,
the OOM killer terminates PHP-FPM workers causing 502 errors.

Swap on root (7.4GB free) not persistent volume — recreated each boot.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: edwh

.fly/scripts/startup.sh

@@ -9,6 +9,16 @@ mkdir -p /var/www/storage/logs
 mkdir -p /var/www/bootstrap/cache
 chown -R www-data:www-data /var/www/storage /var/www/bootstrap/cache
 
+# Create swap file on root filesystem (ephemeral, recreated each boot)
+SWAPFILE=/swapfile
+if [ ! -f "$SWAPFILE" ]; then
+    echo "Creating 4GB swap file..."
+    dd if=/dev/zero of="$SWAPFILE" bs=1M count=4096 2>/dev/null
+    chmod 600 "$SWAPFILE"
+    mkswap "$SWAPFILE"
+fi
+swapon "$SWAPFILE" 2>/dev/null || true
+
 # Ensure log directories exist on the persistent volume (/var/log is mounted)
 mkdir -p /var/log/nginx
 mkdir -p /var/log/sysstat