README, TODO and the viewport README say what the tree does (closes #24)

README.md: Getting Started leads with make targets; a Backend section
gives netwatch-server's routes and how the image builds and runs it;
the checks are GET requests; the WAN host list, health states, summary
figures, sorting and missing features match src/main.js; the TODO
section points to TODO.md, which holds the one to-do list.

backend/README.md: its TODO section points to TODO.md too, whose
Future Steps take its three open items.

TODO.md: Workflow branches from next and opens the PR against next;
Status, Next Step and Future Steps describe the open work, linked to
its issue where one exists.

test/viewport/README.md: the unit tests run on Node's test runner,
not vitest.

Model: opus-5-5

TODO.md

@@ -16,16 +16,11 @@ Docker image, and the Gitea workflow `.gitea/workflows/check.yml` runs
 
 # Next Step
 
-Decide whether the repo moves to the layout `REPO_POLICIES.md` gives, with
-`backend/` no longer repeating files from the root
-([#30](https://git.eeqj.de/sneak/netwatch/issues/30)).
+Take "IPv4 only" out of the page's footer, as nothing in the page limits a check
+to IPv4 ([#111](https://git.eeqj.de/sneak/netwatch/issues/111)).
 
 # Completed Steps
 
-- 2026-10-04: the page's footer no longer says "IPv4 only"
-  ([#111](https://git.eeqj.de/sneak/netwatch/issues/111)): each check is a
-  `fetch`, the browser picks IPv4 or IPv6 for each WAN host, and the local
-  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
@@ -389,6 +384,9 @@ Decide whether the repo moves to the layout `REPO_POLICIES.md` gives, with
 
 # Future Steps
 
+- Decide whether the repo moves to the layout `REPO_POLICIES.md` gives, with
+  `backend/` no longer repeating files from the root
+  ([#30](https://git.eeqj.de/sneak/netwatch/issues/30))
 - Run `make frontend-viewport-test` in CI as its own step; it is not part of
   `make check`, as it needs Docker and takes minutes
 - A backend test that posts a report to `POST /api/v1/reports` and checks the

src/main.js

@@ -857,7 +857,7 @@ function buildUI(state) {
       </div>
 
       <footer class="mt-8 text-center text-gray-600 text-xs">
-        <p>Latency measured via GET requests | CORS restrictions may affect some measurements</p>
+        <p>Latency measured via GET requests | IPv4 only | CORS restrictions may affect some measurements</p>
         <p class="mt-2">
           <span class="inline-block w-3 h-3 rounded-full bg-green-500 mr-1 align-middle"></span>&lt;50ms
           <span class="inline-block w-3 h-3 rounded-full bg-lime-500 mr-1 ml-3 align-middle"></span>&lt;100ms