Recover Apple Silicon installs stranded before the ARM package sources policy (#354)

* Recover Apple Silicon installs stranded before the ARM package sources policy

The policy travels inside the omarchy package, and both places that apply
it are out of reach on a machine installed before it: the installer is
over, and the update aborts in dependency resolution before the package
carrying the helper can be replaced. Such a machine cannot upgrade its
way to the fix.

Add fix-arm-packages.sh, which applies the same preparation from outside
the package and then runs the selection. It sources
install/helpers/arm-package-sources.sh rather than restating it, taking
the copy from its own checkout, $OMARCHY_PATH, or /usr/share/omarchy,
and falling back to the published copy when an installed machine has
none of them.

The transaction identifies itself with OMARCHY_UPDATE_PACMAN=1 the way
omarchy-update-system-pkgs does; without it the update guard hook aborts
the recovery on the machine it exists to fix.

* Fix ARM recovery pipe handling

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Co-authored-by: megabyte0x <megabyte0x@users.noreply.github.com>
Co-authored-by: Naeem Malik <malik2015naeem@gmail.com>