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

backend/README.md

@@ -219,9 +219,8 @@ sent to it.
 
 ## TODO
 
-- Add integration test that POSTs a report and verifies the compressed output
-- Add report decompression/query endpoint
-- Add metrics (Prometheus) for buffer size, flush count, report count
+The to-do list, this backend's open work included, is [TODO.md](../TODO.md) at
+the repo root.
 
 ## License