REVERT the drill bump: uptime-kuma back to 2.4.0 (update-arc measurement finished)

Puts the catalog pin back where 5ff36d0 had it. The box is deliberately left running 2.5.0 for the
R-524 half of the measurement -- a box AHEAD of the catalog must read "Naprakesz"/"Up to date" and
its Update must be refused 409, not offered as a downgrade.

catalog_since stays 2026-09-21, NOT restored to 2026-07-18: the catalog-since gate requires
since >= the commit day of any commit that moves an image: line, and a revert is an image move.
Restoring the old date would fail the gate. So this file does not return byte-for-byte to 5ff36d0 --
the image: line does, the date does not, and that is the gate's rule, not a leftover.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

templates/uptime-kuma/docker-compose.yml

@@ -8,7 +8,7 @@
 
 services:
   uptime-kuma:
-    image: louislam/uptime-kuma:2.5.0
+    image: louislam/uptime-kuma:2.4.0
     container_name: uptime-kuma
     restart: unless-stopped
     environment: