chore: prepare v23.1.8 release

Bump version metadata, refresh manpages, regenerate the example dash.conf
with stable -par/-parbls help text (via #7394), update Flatpak metainfo,
and archive current release notes.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: thepastaclaw

configure.ac

@@ -2,7 +2,7 @@ AC_PREREQ([2.69])
 dnl Don't forget to push a corresponding tag when updating any of _CLIENT_VERSION_* numbers
 define(_CLIENT_VERSION_MAJOR, 23)
 define(_CLIENT_VERSION_MINOR, 1)
-define(_CLIENT_VERSION_BUILD, 7)
+define(_CLIENT_VERSION_BUILD, 8)
 define(_CLIENT_VERSION_IS_RELEASE, true)
 define(_COPYRIGHT_YEAR, 2026)
 define(_COPYRIGHT_HOLDERS,[The %s developers])