README states what refused reports, one sender and nginx's 413 do (closes #145, closes #146, closes #147)

The README said the page keeps refused samples and sends them later.
They live only in the 100-round history, so at the 1-second interval
one refused or failed report loses the oldest 20 seconds of each host's
samples, and a pause longer than the history loses everything since the
last delivered report. Report limits now says one address at the
defaults can fill the 1 GiB cap in about 17 minutes with reports made to
compress badly, and which settings bound it. In the image, nginx's
default client_max_body_size of 1 MiB answers an over-limit body with
413 and an HTML page before the backend sees it; the backend's own 413
sentences now say they apply to it run on its own.

Model: opus-5-5

TODO.md

@@ -21,6 +21,21 @@ Run `make frontend-viewport-test` in CI as its own step; it is not part of
 
 # Completed Steps
 
+- 2026-10-18: `README.md` says what the page loses while reports are refused or
+  the page is paused ([#145](https://git.eeqj.de/sneak/netwatch/issues/145)),
+  how fast one address can replace the stored reports
+  ([#146](https://git.eeqj.de/sneak/netwatch/issues/146)), and that in the image
+  nginx answers a body over 1 MiB itself
+  ([#147](https://git.eeqj.de/sneak/netwatch/issues/147)). A sample not yet
+  delivered is kept only as long as the history holds it: at the 1-second
+  interval one refused or failed report loses the oldest 20 seconds of each
+  host's samples, and a pause longer than the history loses every sample since
+  the last delivered report. At the defaults, one address sending 1 MiB reports
+  made up to compress badly can fill the 1 GiB cap in about 17 minutes. nginx's
+  `client_max_body_size` is also 1 MiB by default, so in the image it answers a
+  larger body with 413 and its own HTML page, and the backend never sees or
+  records it; the backend's own 413 sentences now say they apply to it run on
+  its own. The reporter, the body limit and nginx are unchanged
 - 2026-10-18: a browser that cannot format the header's clocks still probes
   ([#149](https://git.eeqj.de/sneak/netwatch/issues/149)). The clocks name the
   local time zone through `Intl.DateTimeFormat`'s `shortGeneric` option, which