Align the China region to the official cn profile

The region value is cn, the China files live under default/regions/cn/, and
omarchy-apply-pacman renders pacman for every caller: the .cn twins of the
channel servers first, then .org, USTC and ArchLinuxCN. Switching to China
installs and trusts the ArchLinuxCN keyring. A migration renames china to cn
and repoints the drop-in links.

test/shell.d/region-pacman-test.sh

@@ -32,18 +32,19 @@ for channel in stable rc edge; do
     edge) host=mirror.omarchy.org ;;
   esac
   apply "$channel"
-  expected=$(printf 'Server = https://%s/$repo/os/$arch\nServer = https://mirrors.ustc.edu.cn/archlinux/$repo/os/$arch' "$host")
+  expected=$(printf 'Server = https://%s/$repo/os/$arch\nServer = https://%s/$repo/os/$arch\nServer = https://mirrors.ustc.edu.cn/archlinux/$repo/os/$arch' "${host%.org}.cn" "$host")
   [[ $(<"$TARGET_ROOT/etc/pacman.d/mirrorlist") == "$expected" ]] || fail "$channel mirror order and variables"
   {
-    cat "$ROOT/default/pacman/pacman-$channel.conf"
+    sed -f "$ROOT/default/regions/cn/pacman/servers.sed" "$ROOT/default/pacman/pacman-$channel.conf"
     printf '\n[archlinuxcn]\nServer = https://mirrors.ustc.edu.cn/archlinuxcn/$arch\n'
   } > "$scratch/expected.conf"
+  grep -qx "Server = https://pkgs.omarchy.cn/$channel/\$arch" "$scratch/expected.conf" || fail "$channel lists the .cn Omarchy repository"
   cmp "$scratch/expected.conf" "$TARGET_ROOT/etc/pacman.conf"
   apply "$channel"
   cmp "$TARGET_ROOT/etc/pacman.conf.bak" "$TARGET_ROOT/etc/pacman.conf"
   cmp "$TARGET_ROOT/etc/pacman.d/mirrorlist.bak" "$TARGET_ROOT/etc/pacman.d/mirrorlist"
 done
-pass "China keeps each channel first, appends only CN defaults, and is idempotent"
+pass "China puts a .cn twin ahead of each channel server, appends the CN defaults, and is idempotent"
 
 cp "$TARGET_ROOT/etc/pacman.conf" "$scratch/before.conf"
 cp "$TARGET_ROOT/etc/pacman.d/mirrorlist" "$scratch/before.mirrors"
@@ -75,7 +76,7 @@ mkdir -p "$scratch/rendered"
 "$ROOT/bin/omarchy-apply-pacman" --render rc "$scratch/rendered" "$TARGET_ROOT"
 rg -qxF 'Server = https://pkgs.omarchy.org/rc/$arch' "$scratch/rendered/pacman.conf"
 rg -qxF '[archlinuxcn]' "$scratch/rendered/pacman.conf"
-[[ $(<"$scratch/rendered/mirrorlist") == $'Server = https://rc-mirror.omarchy.org/$repo/os/$arch\nServer = https://mirrors.ustc.edu.cn/archlinux/$repo/os/$arch' ]] ||
+[[ $(<"$scratch/rendered/mirrorlist") == $'Server = https://rc-mirror.omarchy.cn/$repo/os/$arch\nServer = https://rc-mirror.omarchy.org/$repo/os/$arch\nServer = https://mirrors.ustc.edu.cn/archlinux/$repo/os/$arch' ]] ||
   fail "render keeps the channel mirror first"
 cmp "$scratch/before.conf" "$TARGET_ROOT/etc/pacman.conf"
 pass "render builds the regional channel files without touching the target"