www/mybb: Update 1.8.39 => 1.8.40 (18 security vulnerabilities), take maintainership

Release Notes
https://blog.mybb.com/2026/05/28/mybb-1-8-40-released-security-maintenance-release/

Improve port:

• Update WWW - old link redirects to new.
• Fix warnings from portclippy.
• Sort USE_PHP.
• Remove unnecessary WWWDIR - it have default value.
• Replace "CP -R" with "COPYTREE_SHARE".

PR: 295713
Security: GHSA-p766-qqxv-rfc2
Security: GHSA-4p6g-p3qh-559v
Security: GHSA-gpc4-77rp-3xqr
Security: GHSA-wf92-5q5h-qr53
Security: GHSA-p48q-4vgf-q7x8
Security: GHSA-c2hm-g9w6-pv6x
Security: GHSA-r25v-7pcm-q34p
Security: GHSA-w8gm-j57p-jqpc
Security: GHSA-839m-gpw8-59j4
Security: GHSA-gfxj-g7w6-6w4v
Security: GHSA-56wr-64wx-5g7j
Security: GHSA-f626-53q9-pqm9
Security: GHSA-75vg-6wgp-mcc9
Security: GHSA-m42q-vgx3-fqcc
Security: GHSA-m6hr-25cj-p58q
Security: GHSA-xx78-g79m-qvgq
Security: GHSA-jrrr-f3jw-mjmc
Security: GHSA-v2h7-4jp7-j6hh
Sponsored by: UNIS Labs
Co-authored-by: Vladimir Druzenko <vvd@FreeBSD.org>
MFH: 2026Q2

(cherry picked from commit 985692ee87a985044c25b05e709a55ca0451cae0)