Rewrite the root README as a short, non-technical project overview

The old file was a confusing mix of eras: an accurate current
Windows/Rocky/VPS environment section sitting alongside stale leftovers
from before this project's current setup existed -- a wrong port (9090,
staging is actually 9190), old docker-compose v1 syntax, a podman-compose
three-terminal dev loop nobody uses, an nginx config for laikazinas.lsm.lv
(the real current LSM production site, unrelated to and confusable with
this project's actual temporary test domain), Fly.io commands from a
hosting platform no longer in use, and an example command that happens to
run one of the files this session's security review flagged as a
mislabeled test script capable of touching a live database.

Replaced with a short landing page: what the tool does, how it's built,
current status (Rocky-only development now that Windows is retired from
the workflow, laikapstak.li as the temporary test environment ahead of
eventually replacing the live laikazinas.lsm.lv service), and a security
summary -- all pointing to docs/ for actual technical depth rather than
duplicating half-true instructions. Updated docs/README.md's own
description of the root README to match.

docs/README.md

@@ -1,6 +1,6 @@
 # WeatherTool project documentation
 
-This directory contains the working documentation for the WeatherTool modernization effort. The repository-root `README.md` is preserved as the original project overview; these documents describe the reviewed code, current staging environment, and changes being developed.
+This directory contains the working documentation for the WeatherTool modernization effort. The repository-root `README.md` is a short, non-technical overview for anyone landing on the repo (purpose, status, security posture); these documents describe the reviewed code, current staging environment, and changes being developed in full technical depth.
 
 ## Current status