Fix ARM64 pacman.conf: SigLevel = Never for mirror reliability

ALARM mirrors inconsistently serve .db.sig files — some mirrors return
404 for core.db.sig which aborts the pacstrap. SigLevel = Never is
standard practice for Docker-based archiso builds.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/docker/entrypoint-arm64.sh

@@ -23,6 +23,8 @@ cat > "$PROFILE/pacman.conf" <<'PACMANCONF'
 [options]
 HoldPkg     = pacman glibc
 Architecture = aarch64
+# Mirrors occasionally lack .db.sig files — disable sig checks for reliability
+SigLevel    = Never
 
 [core]
 Include = /etc/pacman.d/mirrorlist