Verify each finding against the current code and only fix it if needed.

Inline comments:
In @.github/helper/install.sh:
- Around line 47-50: The current early return when installing the .deb for
wkhtml_package gets bypassed by set -e because failures abort the script; change
the logic around the wkhtml_package block so the wget + apt install attempt is
tried but does not exit the script on failure—capture the commands' exit status
and only return when they succeed (e.g., run wget and sudo apt install for the
variable wkhtml_package, check their exit codes, and if both succeed then
return; otherwise continue to the tarball fallback). Ensure you reference the
wkhtml_package variable and the block that currently does wget -O
"/tmp/${wkhtml_package}" ... and sudo apt install ... "/tmp/${wkhtml_package}"
and replace the unconditional return with a conditional return based on success.

In `@README.md`:
- Around line 96-98: The fenced shell code block contains a leading shell prompt
character ('$') before the command 'bench start' which violates markdownlint
rule MD014; remove the leading '$' so the block contains just the raw command
(i.e., replace "$ bench start" with "bench start" in the fenced code block) to
satisfy the linter while keeping the command example intact.