say so when installing a site without its images

say so when installing a site without its images

brisk-img carries every image of the site: the cards, the table, the
icons. INSTALL.sh picks it up from beside this repository, and when it is
not there it used to skip it without a word - so a run that had quietly
dropped every image looked exactly like a good one, and the site came up
with each img answering 404.

That is how this went unnoticed: the bench was moved into the container
with only the brisk repository mounted, brisk-img was left outside, and
several runs of INSTALL.sh rebuilt the tree without images while
reporting success.

It now warns, and says what to do about it. curl-de-sac gets a milder
note on the same spot: the code that uses it is guarded by
defined('CURL_DE_SAC_VERS'), so without it the feature is simply absent
rather than broken.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Fseposbqj9mBbQXoT8KnBj