Reserved custom slugs

A custom slug in this list is rejected with HTTP 409 and error code reserved_slug.
The list is the RESERVED_SLUGS set in src/pages/api/short-links.ts.
Matching is case-insensitive because the slug is lowercased before the check.

about
account
admin
api
assets
contact
create
dashboard
delete
edit
en
favicon
health
help
login
logout
mail
new
privacy
pt
register
robots
s
settings
short-links
sign-in
sign-up
sitemap
static
support
terms
tool
tools
url-shortener
www
_astro