packaging: bare backticks — a heredoc's backslash isn't the JSON's

Run 2981 built everything and then died posting the release: HTTP 422,
"invalid escape sequence \`". The body's other backticks are written \` because
they sit in an UNQUOTED heredoc, where that backslash is the shell's and is gone
before any JSON exists. Copying the idiom into a single-quoted variable changed
what it meant — single quotes already stop substitution, so the backslash
survived into the body as an escape JSON has no rule for.

bash -n passes either way; it checks syntax, not what a string becomes. So parse
the assembled body for every branch it can take instead, and write down the
recipe next to the one for formatting Rust.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MKsUY9Z45KQd34V956hZ9Q

desktop/packaging/publish-release.sh

@@ -100,7 +100,11 @@ first_id() { grep -oE '"id"[[:space:]]*:[[:space:]]*[0-9]+' | head -1 | grep -oE
 # wonders why the version they were sent isn't what they got.
 if [ "$TAG" = "dev" ]; then
   INSTALL_TAIL='sh -s -- --channel dev'
-  CHANNEL_NOTE='\n\nThis is the rolling **dev** channel: republished on every green push to \`dev\`, and pruned to the current build.'
+  # Backticks BARE, not `\``. The heredoc below is unquoted, so there the backslash
+  # is the shell's — it suppresses command substitution and never reaches the JSON.
+  # Here single quotes already do that job, so a backslash would survive into the
+  # body as `\``, which is not a legal JSON escape: Forgejo answers 422.
+  CHANNEL_NOTE='\n\nThis is the rolling **dev** channel: republished on every green push to `dev`, and pruned to the current build.'
 else
   INSTALL_TAIL='sh'
   CHANNEL_NOTE=''