Hold back blocking packages instead of failing the whole upgrade

A repo package that replaces something an installed AUR package still depends
on aborted the entire transaction, and would have done so on every subsequent
run - one stale AUR package was enough to cut a machine off from all updates
indefinitely. Observed in the wild: percona-server-clients replaces
libperconaserverclient without providing it, while heidisql-qt6-bin hard-depends
on it, blocking 213 unrelated package updates.

pacman names the offending package in its dependency errors, so it is now
extracted and passed to --ignore for one retry: the other 213 packages go
through and the blocker is reported. The hold is per-run, never written to
IgnorePkg, so it disappears by itself once upstream catches up.

The single retry is also now a bounded recovery loop, because fixing one
problem regularly uncovers the next - a conflict resolved with --ask=20 can
surface a dependency error behind it. Each remedy is applied at most once.

The held-back set is shown in the menu and notified only when it changes, so a
blocker waiting on an upstream fix does not produce the same message daily.

po/cachy-auto-update.pot

@@ -243,3 +243,14 @@ msgstr ""
 
 msgid "pacman's lock file looks left over from an interrupted update. Updates are paused until it is cleared."
 msgstr ""
+
+msgid "Some packages were held back"
+msgstr ""
+
+#, c-format
+msgid "%s could not be updated and was skipped. Everything else is up to date."
+msgstr ""
+
+#, c-format
+msgid "Held back: %s"
+msgstr ""