An installer that moved a channel nobody asked it to

The channel lives in two places -- lembas.env, which the page reads, and
the systemd unit, which the button obeys -- and a re-run keeps the env
file while rewriting the unit. Defaulting to stable therefore meant a
re-run for some unrelated reason silently moved one half and not the
other, leaving a host whose page named edge and whose button deployed
stable.

That mismatch already had an alert. An installer that causes the thing it
detects is the wrong end to be detecting it from, so it defaults to what
the host already follows. Parsed rather than sourced: that file holds the
secret key.

Found by running it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -51,6 +51,12 @@ and did not.
   ownership boundary through a field that looks like a tag.
 - Fixed: a `"` typed into the share panel's search box silently stopped every
   checkbox in the panel from doing anything.
+- Fixed: **re-running the installer moved the update channel to `stable`** even
+  on a host following `edge`. The channel lives in two places — the environment
+  file the page reads and the systemd unit the button obeys — and a re-run kept
+  the first while rewriting the second, so an install for some unrelated reason
+  left the page naming one channel and the button deploying another. It now
+  defaults to what the host already follows.
 
 ## 0.9.11