Proposal: shared email_greeting()/email_footer() helpers for consistent plain-text emails

[FraSanga]

Summary

Stock html/inc/email.inc and the various send_*_email() functions across the codebase have no
shared header/footer, and the result is inconsistent from one email to the next. Some examples from
the current code:

• send_auth_email() ends with a "For further information and assistance with PROJECT, visit ..."
  block.
• send_thread_notification_email()/send_forum_notification_email() end with a different
  "--------------------------\nTo change email preferences, visit:\n...\nDo not reply to this
  message." block.
• send_moderation_email(), send_thread_moderation_email(), send_banish_email(),
  send_banish_vote_email() have no footer at all — the message just stops.
• None of them open with any kind of greeting.

On our own project (Camicia) we put together a small shared pair of helpers to fix this:

function email_greeting($user) {
    return "Hi $user->name,\n";
}

function email_footer($prefs_link = true) {
    $footer = "\n--\n".PROJECT."\n".secure_url_base()."\n";
    if ($prefs_link) {
        $footer .= "\nTo change your email preferences, visit:\n"
            .secure_url_base()."edit_forum_preferences_form.php"
            ."\nDo not reply to this message.\n";
    }
    return $footer;
}

email_greeting() for the opening line (only used for emails going to a real named recipient, not
role-addressed ones like POST_REPORT_EMAILS), and email_footer($prefs_link) for the closing
block — $prefs_link gated because emails to project/team admins aren't gated by their forum
notification preferences, so it doesn't make sense to point them at that page.

Applied across email.inc, forum_email.inc, friend.inc, pm.inc, uotd.inc, ops/notify.php,
ops/manage_user.php, ops/team_import.php, and user/team_founder_transfer_action.php — every
send_*_email() we could find. Along the way this also surfaced two real bugs already reported/fixed
separately (#7311/#7312, and a dead-code duplicate $subject assignment in
send_thread_moderation_email()).

Question for maintainers

Is this worth contributing back, and if so, at what scope? A few things in what we did are more a
matter of taste than a fix, and we'd rather ask first than send a big diff that assumes the answer:

1. The helpers + consistent usage (the part above) seems like a plain improvement regardless of
   project — happy to open a PR for just this if it's wanted.
2. We also changed subject lines from "[PROJECT] x" to "PROJECT: x" for consistency — purely
   cosmetic, easy to drop if you'd rather keep the brackets.
3. For emails that currently go to both a named user and an admin/moderator list with the same
   body (e.g. send_banish_email(), send_moderation_email()), we split them into a personal
   greeting+footer version for the user and a separate third-person version for admins. This is more
   than styling — it changes what admins actually see — so it may be worth its own separate
   discussion regardless of whether 1) is wanted.

Happy to open PR(s) for whichever of these make sense, scoped however's easiest to review.

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Drafted with AI assistance (Claude, Anthropic) per the project's AI Assistants Usage Policy.