Make aarch64 a first-class architecture in the scheduled pipeline

One list, PUBLISHED_ARCHES in helpers/paths.sh (default x86_64,
overridable with OMARCHY_ARCHES), now drives everything the repository
host schedules. check-versions compares PKGBUILDs against each
architecture's channel databases and writes one queue per channel and
architecture; auto-release works through the queues one architecture at
a time, each with its own backoff, so a failing build on one never
blocks the other; advance-channel --arch all re-runs an advance for every
published architecture and omarchy-release uses it for start and ship,
building the pinned pair once per architecture in its rc trigger; the
train observes channels through the reference (first) architecture
instead of a hard-coded x86_64. Queue and backoff files written under
the old per-channel names are treated as x86_64 until consumed.

Two things made an aarch64 builder image impossible to create: the
keyring bootstrap fetched omarchy-keyring from the target architecture's
own channel tree, which does not exist before that architecture has
published anything, and the QEMU probe only knew the x86_64-host,
aarch64-target case. The keyring (arch=any) now always comes from the
x86_64 tree, and the probe compares host and target architectures and
runs a container for the target platform.

clean-repo grouped versions with a regex that only knew any, x86_64 and
i686, so aarch64 packages would never have been pruned.

bin/setup

@@ -237,6 +237,10 @@ echo ""
 
 # --- release timers ----------------------------------------------------------
 
+print_info "Published architectures: $(published_arches | tr '\n' ' ')"
+echo "    (PUBLISHED_ARCHES in helpers/paths.sh, or OMARCHY_ARCHES in $CREDENTIALS)"
+echo ""
+
 TIMERS=(omarchy-check-versions omarchy-auto-release-edge omarchy-auto-release-rc omarchy-auto-release-stable)
 
 if [[ "$SKIP_TIMERS" == true ]]; then