Revert "Say that a deploy keeps only an app's volumes when the app has none"

This reverts commit cc786a1e84, at the
owner's request. It removes the app page sentence for an app with no
volume mounts, the matching deploy log line and its constant, their
tests, the README sentence and the TODO.md entry. The environment
variable hint keeps its alert-warning class, which is in the committed
stylesheet.

Model: opus-5-5

TODO.md

@@ -38,11 +38,6 @@ regress.
   style, instead of asking for a container restart, which keeps the old values
   (#255).
 
-- 2026-10-01: An app with no volume mounts says on its page, and in the log of
-  each deploy, that a deploy or rollback loses the files it writes and a restart
-  keeps them; the README's Volume mounts section says a deploy or rollback keeps
-  only the files the app wrote to its volume mounts (#248).
-
 - 2026-10-01: Builds attach a BuildKit session, as the docker command line does,
   so a base image that is not on the host is pulled instead of the build failing
   with "no active sessions" on Docker Engine 27. Container logs, and so the