Resolve "feat: add ahikar.css file to backend"

Closes #266 (closed)

the file itself was included to the exist-app before, but not used there. instead during the ant build we got it from the olde git repo "ahikar-tido". during post-install it is copied to a collection exposed via rest. in addition a restxq endpoint serves the file.

(also i did some renaming ahikar → ahiqar).