fix: add missing space to mail footer signature delimiter

[DeepDiver1975]

Description

The signature delimiter on the first line of the mail footer templates was missing the trailing space required by the signature block convention (RFC 3676). The delimiter must be exactly -- (dash-dash-space) followed by a line break for mail clients to recognize and collapse the signature.

• core/templates/plain.mail.footer.php: -- → --
• core/templates/html.mail.footer.php: --<br> → -- <br>

How was this tested?

• Verified the exact bytes of line 1 in both files (cat -A shows -- $ and -- <br>$).
• Confirmed php-cs-fixer does not strip the trailing space: although the coding standard enables no_trailing_whitespace and these templates are not excluded, line 1 is an inline-HTML token (T_INLINE_HTML) which the rule does not touch — dry-run reports 0 of 2 files to fix.
• php -l passes on both templates.

Fixes #41364

🤖 Generated with Claude Code

[phil-davis]

Is it OK that this changelog file is named 41364 but the PR is now 41617?

[DeepDiver1975]

Good catch — I've renamed the file to 41617 to match the PR number and added the PR link alongside the issue link. Thanks!

[DeepDiver1975]

Code Review

Overview: Single-character fix — adds the trailing space to the email footer signature delimiter in both the HTML and plain-text mail footer templates.

The fix: -- → -- (dash-dash-space). This is the correct RFC 3676 / email convention signature delimiter. Mail clients (Thunderbird, Mutt, etc.) recognize -- \n as the separator between message body and signature and use it to visually collapse or style the signature block. Without the trailing space, clients treat it as body text.

Files changed:

• core/templates/html.mail.footer.php — ---<br> → -- <br> (also removes the erroneous third dash)
• core/templates/plain.mail.footer.php — --- → -- (same correction)

Note: The HTML template previously had three dashes (---), which was doubly wrong. This fix corrects both the dash count and the missing space in one change.

Changelog entry: changelog/unreleased/41364 is well-written and correctly references the RFC 3676 convention.

No concerns. Clean minimal fix.