Never mistake an entry edited in place for one we generated

A desktop entry that already lives in ~/.local/share/applications is the
user's own file, patched in place with the original kept aside. It used to
get the same X-MCA-Generated marker as a shadow copy, which made the next
scan skip it, fall back to the system entry, and overwrite the user's file
with a shadow - and then delete it on revert instead of restoring it.

The two cases now carry different markers. Only a shadow is skipped by the
scan and deleted when undoing; an entry patched in place stays in the scan
and is restored from its backup.

Also: resolve the applications screen's labels once instead of per row per
keypress, and drop code nothing calls.

po/middleclick-autoscroll.pot

@@ -4,7 +4,7 @@
 #
 msgid ""
 msgstr ""
-"Project-Id-Version: middleclick-autoscroll 1.0.0\n"
+"Project-Id-Version: middleclick-autoscroll 1.0.1\n"
 "Report-Msgid-Bugs-To: https://github.com/Felitendo/middleclick-autoscroll/issues\n"
 "POT-Creation-Date: 2026-08-16 00:00+0200\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"