Allowlist no host in the example config (closes #249)

configs/config.example.yml allowlisted github.com and
user-images.githubusercontent.com, where anyone can put an image, so a
deployment set up as Getting Started says served those images to anyone
without a signature. The example now leaves allowlist_hosts out, with
one commented entry under example.com. Getting Started and "Running
under upaas" in README.md say that every image on an allowlisted host
is served without a signature, so an allowlisted host must be one the
operator controls.

Model: opus-5-5

TODO.md

@@ -30,6 +30,14 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-15 the example config allowlists no host (closes #249): it allowlisted
+  `github.com` and `user-images.githubusercontent.com`, where anyone can put an
+  image, so a deployment set up as Getting Started says served those images to
+  anyone without a signature, at any size and in any format.
+  `configs/config.example.yml` now leaves `allowlist_hosts` out, with one
+  commented entry under `example.com`. Getting Started and "Running under upaas"
+  in `README.md` say that every image on an allowlisted host is served without a
+  signature, so an allowlisted host must be one the operator controls.
 - 2026-10-13 `fit=outside` no longer makes an output above 8192 on a side
   (closes #257): it scales the image to cover the requested size, and the side
   scaled past that size was held to no maximum, so `1x8192?fit=outside` of a