Extract pkg cmd abstractions and clean up all migrations (#1291)

* No using custom chromium.desktop any more

* Spacing

* Rely on $OMARCHY_PATH

* Add common pkg and cmd functions for use in migrations and elsewhere

* Simple pkg-adds

* Later migration does it

* Ensure running migrations on older installs have the new pkg/cmds available

* Spacing

* Use new abstractions

* Installed in later migration

* Needless comment

* Use new commands

* Fix package name from 'batt' to 'bat'

migrations/1751672984.sh

@@ -1,5 +1,3 @@
 echo "Add LocalSend as new default application"
 
-if ! command -v localsend &>/dev/null; then
-  sudo pacman -S --noconfirm --needed localsend
-fi
+pkg-add localsend