Health box and summary update as each WAN check ends (closes #206)

The health box and the summary were drawn only once every check in a
round had ended, so a target that never answers held them back until
its timeout, after the rows already showed the network was back. tick
now redraws both with each WAN host's row. The "Health:" debug log line
moved from updateHealthBox to the end of the round, so it is still
written once per round, and still only once a WAN host's check is
recorded.

Model: opus-5-5

README.md

@@ -107,6 +107,9 @@ Below it, a summary line covers the WAN hosts only:
   history
 - `Checks`: the rounds run since the page loaded or the interval changed
 
+The health box and the summary take in a WAN host's result as soon as its row
+shows it.
+
 When no WAN host answers, the page checks 4 of them, picked at random, every
 half second. As soon as one answers, a new round starts.
 
@@ -363,7 +366,8 @@ The page is built with Vite and Tailwind CSS v4. All its code is in
 - `HostState` and `AppState`: one host's history and status, and the whole
   page's state.
 - `measureLatency`: one check. `tick`: one round, which checks every host in
-  parallel and draws each row as soon as its check ends.
+  parallel. It draws each row as soon as its check ends, and with a WAN host's
+  row also the summary and the health box.
 - `SparklineRenderer`: the graphs. `buildUI`, `updateHostRow`, `updateSummary`
   and `updateHealthBox`: the page and its parts.
 - `Reporter`: builds and posts the reports. `buildReport` is a pure function of