fix: FileBrowser default dirs, login option on onboarding intro

- Pre-create Documents/Photos/Music/Downloads/Builds dirs for FileBrowser
- Add "Already set up? Log in" link on onboarding intro page
- Prevents users from getting stuck in onboarding loop

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

scripts/first-boot-containers.sh

@@ -949,6 +949,8 @@ track_container "searxng"
 if ! $DOCKER ps --format '{{.Names}}' 2>/dev/null | grep -q filebrowser; then
   log "Creating File Browser..."
   mkdir -p /var/lib/archipelago/filebrowser /var/lib/archipelago/filebrowser-data
+  # Pre-create default directories so FileBrowser doesn't 404 on first load
+  mkdir -p /var/lib/archipelago/filebrowser/{Documents,Photos,Music,Downloads,Builds}
   $DOCKER run -d --name filebrowser --restart unless-stopped \
     --health-cmd="curl -sf http://localhost:80/ || exit 1" --health-interval=120s --health-timeout=5s --health-retries=3 \
     --memory=$(mem_limit filebrowser) \