release: 2.4.2: audit stage 0, release hygiene

Stage 0 of docs/audit-2026-10-12.md, 7/7: the release image says which
release it is (H1), the e2e module is compiled on every push (M20),
test/ is out of the build context (L33), the documents say the 2.x image
is not published and show the local build (M6), dependencies raised,
staticcheck clean, the negative e2e cases held to their own refusals
(which showed the level-1 rate-limit case had never seen the limit).

CHANGELOG cut; pin 2.4.2 in deploy/docker-compose.yml, README (with the
local-build note), guide; development.md "from pin" and the planned cuts
of the audit's stages (2.5.0 ... 2.6.0); roadmap row in progress and the
recommended order; stage 0 marked shipped in the plan. No tag (the
owner's command only).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,12 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ## [Unreleased]
 
+## [2.4.2] - 2026-10-14
+
+Release hygiene: stage 0 of the 2026-10-12 audit. Nothing the panel or the
+mail path does changes; the release workflow, the tests, the dependencies and
+the documents do.
+
 ### Fixed
 
 - **A release image says which release it is.** The e2e gate in