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/timers

@@ -84,15 +84,18 @@ echo ""
 
 # --- queued work -------------------------------------------------------------
 
-print_info "Queued builds (state files in $STATE_DIR)"
+print_info "Queued builds (state files in $STATE_DIR; architectures: $(published_arches | tr '\n' ' '))"
 queued=false
 for channel in edge rc stable; do
-  state_file="$STATE_DIR/.sync-needed-$channel"
-  if [[ -f "$state_file" ]]; then
-    queued=true
-    since=$(date -r "$state_file" '+%Y-%m-%d %H:%M:%S' 2>/dev/null || echo "unknown")
-    printf '  • %-7s queued since %s\n' "$channel" "$since"
-  fi
+  for arch in $(published_arches); do
+    state_file=$(sync_queue_file "$channel" "$arch")
+    [[ "$arch" == "x86_64" && ! -f "$state_file" ]] && state_file=$(legacy_sync_queue_file "$channel")
+    if [[ -f "$state_file" ]]; then
+      queued=true
+      since=$(date -r "$state_file" '+%Y-%m-%d %H:%M:%S' 2>/dev/null || echo "unknown")
+      printf '  • %-7s %-8s queued since %s\n' "$channel" "$arch" "$since"
+    fi
+  done
 done
 [[ "$queued" == false ]] && echo "  (nothing queued — all channels up to date)"
 echo ""
@@ -101,7 +104,9 @@ echo ""
 # say so plainly: it is queued but deliberately not being retried yet.
 paused=false
 for channel in edge rc stable; do
-  fail_file="$STATE_DIR/.build-failed-$channel"
+  for arch in $(published_arches); do
+  fail_file=$(sync_fail_file "$channel" "$arch")
+  [[ "$arch" == "x86_64" && ! -f "$fail_file" ]] && fail_file=$(legacy_sync_fail_file "$channel")
   [[ -f "$fail_file" ]] || continue
   if [[ "$paused" == false ]]; then
     print_error "Failing builds (backoff active)"
@@ -122,13 +127,14 @@ for channel in edge rc stable; do
   else
     when="retries on the next tick"
   fi
-  printf '  ✗ %-7s %s consecutive failure(s), %s\n' "$channel" "$FAILURE_COUNT" "$when"
+  printf '  ✗ %-7s %-8s %s consecutive failure(s), %s\n' "$channel" "$arch" "$FAILURE_COUNT" "$when"
   printf '      last attempt %s on commit %s\n' \
     "$(date -d "@$FAILURE_AT" '+%Y-%m-%d %H:%M:%S' 2>/dev/null || echo "$FAILURE_AT")" \
     "${FAILURE_FINGERPRINT:0:12}"
+  done
 done
 if [[ "$paused" == true ]]; then
-  echo "  Any new commit clears the backoff; or: rm $STATE_DIR/.build-failed-<channel>"
+  echo "  Any new commit clears the backoff; or: rm $STATE_DIR/.build-failed-<channel>-<arch>"
   echo ""
 fi