ip rule pref is otherwise derived from alphabetical group order, so a group
cannot be consulted before a lexicographically-earlier one (e.g. fr vs egw)
without renaming it — and digits sort after letters in ru_RU.UTF-8, so even
a '0-fr' rename goes the wrong way.

Allow an options line "pref N" to set the group's pref base directly,
independent of name or locale. Used on fr (pref 900) so claude.ai via fr
wins over the egw/ai table (pref 1210).

Also call _fixup_rule_pref on the "resolved unchanged" skip path, so an
options-only change actually migrates the ip rule to the new pref (previously
the rule kept its old pref because load was skipped).
Co-Authored-By: Claude <noreply@anthropic.com>