Rewrite the README sentence by sentence

The README is rewritten from scratch against the prose rules of
#157: every sentence under
about 30 words, lists as bullets, every technical term defined where it
first appears, and every statement checked against the code on next. It
leads with what RouteWatch is and how to run it, then the pages, the API
and the blocklists, then the settings, memory and upaas, and last the
design and the development workflow. The dated entry goes into TODO.md.

Model: fable-5-1

TODO.md

@@ -35,6 +35,12 @@ tested.
 
 # Completed Steps
 
+- 2026-11-02: `README.md` rewritten from scratch, sentence by sentence, against
+  the rules of https://git.eeqj.de/sneak/routewatch/issues/157. It leads with
+  what RouteWatch is and how to run it, then the pages and the API, then the
+  settings, memory and upaas, and ends with the design and development. Every
+  statement was checked against the code (part of
+  https://git.eeqj.de/sneak/routewatch/issues/157)
 - 2026-10-27: the tests of `internal/routewatch` no longer fail on a loaded
   host. Five of them gave `HandleMessage` two seconds to apply a full prefix
   batch, which under the race detector can take longer. A test now waits up to