Footer no longer says IPv4 only (closes #111)

Each check is a fetch: the browser picks IPv4 or IPv6 for each WAN
host, and the local targets are IPv4 addresses, so "IPv4 only" was
wrong for the page as a whole. The footer's first line drops it and
its separator; the rest of the footer is unchanged. TODO.md moves this
to Completed Steps and the layout decision from Future Steps into Next
Step.

Model: opus-5-5

TODO.md

@@ -23,9 +23,9 @@ Decide whether the repo moves to the layout `REPO_POLICIES.md` gives, with
 # Completed Steps
 
 - 2026-10-04: the page's footer no longer says "IPv4 only"
-  ([#111](https://git.eeqj.de/sneak/netwatch/issues/111)), as nothing in the
+  ([#111](https://git.eeqj.de/sneak/netwatch/issues/111)): each check is a
-  page limits a check to IPv4: each check is a `fetch`, and the browser picks
+  `fetch`, the browser picks IPv4 or IPv6 for each WAN host, and the local
-  IPv4 or IPv6 for each target. The rest of the footer is unchanged
+  targets are IPv4 addresses. The rest of the footer is unchanged
 - 2026-10-04: `README.md`, `TODO.md` and `test/viewport/README.md` say what the
   tree does (issue #24). The README's Getting Started leads with `make` targets;
   a new Backend section says what `netwatch-server` stores, its routes and how