use 12-character commit hashes

[llfw]

currently mfctracker uses 8-char commit hashes:

56f9879c ivy Oct. 8, 2025, 6:08 a.m. libexec/rc/rc.d/Makefile: Use CONFGROUPS.yes

these are no longer considered unique, and i've encounted at least one case in real life where an 8-character commit id was not unique enough to use with git cherry-pick. we should show the 12-character commit hash instead.

[llfw]

for comparison, the mfc-candidates tool already does this:

2!freebsd15 ..bsd/stable-15 [stable/15]% tools/tools/git/mfc-candidates.lua -u ivy
561dc357c2f5 bsdinstall: Use package sets for pkgbase install