Merge reworked #13690: timezone-derived region and channel mirror prepends

Drop the .cn servers.sed twins, the USTC Arch fallback and the closed
#14399 timezone preselection. region.sh follows the installer's marker.

bin/omarchy-apply-pacman

@@ -53,25 +53,25 @@ else
   trap 'rm -rf "$staging"' EXIT
 fi
 cp "$OMARCHY_PATH/default/pacman/pacman-$channel.conf" "$staging/pacman.conf"
-cp "$OMARCHY_PATH/default/pacman/mirrorlist-$channel" "$staging/mirrorlist"
-if [[ $region != "global" ]]; then
+if [[ $region == "global" ]]; then
+  cp "$OMARCHY_PATH/default/pacman/mirrorlist-$channel" "$staging/mirrorlist"
+else
   profile="$OMARCHY_PATH/default/regions/$region/pacman"
-  # A region's own copies of the channel servers go ahead of them.
-  if [[ -r $profile/servers.sed ]]; then
-    sed -i -f "$profile/servers.sed" "$staging/pacman.conf" "$staging/mirrorlist"
-  fi
   printf '\n' >> "$staging/pacman.conf"
   cat "$profile/pacman.conf.append" >> "$staging/pacman.conf"
-  cat "$profile/mirrorlist.append" >> "$staging/mirrorlist"
+  # pacman tries servers in order, so the regional mirror leads and the
+  # channel's own mirror stays as the fallback.
+  cat "$profile/mirrorlist-$channel.prepend" "$OMARCHY_PATH/default/pacman/mirrorlist-$channel" > "$staging/mirrorlist"
 fi
-[[ -z $render_dir ]] || exit 0
 
-mkdir -p "$etc/pacman.d"
-for file in pacman.conf pacman.d/mirrorlist; do
-  if [[ -e $etc/$file ]]; then
-    cp -f "$etc/$file" "$etc/$file.bak"
-  fi
-done
-# Copying over an existing file keeps its owner and mode, as refresh always has.
-cp -f "$staging/pacman.conf" "$etc/pacman.conf"
-cp -f "$staging/mirrorlist" "$etc/pacman.d/mirrorlist"
+if [[ -z $render_dir ]]; then
+  mkdir -p "$etc/pacman.d"
+  for file in pacman.conf pacman.d/mirrorlist; do
+    if [[ -e $etc/$file ]]; then
+      cp -f "$etc/$file" "$etc/$file.bak"
+    fi
+  done
+  # Copying over an existing file keeps its owner and mode, as refresh always has.
+  cp -f "$staging/pacman.conf" "$etc/pacman.conf"
+  cp -f "$staging/mirrorlist" "$etc/pacman.d/mirrorlist"
+fi

bin/omarchy-channel-set

@@ -55,10 +55,15 @@ validate_dev_region() {
   [[ -f $region_file ]] && region=$(<"$region_file")
   [[ $region == "global" ]] && return 0
 
-  # The refresh after linking needs a runnable helper and both fragments, not
-  # just a directory with the region's name.
-  local profile="$checkout/default/regions/$region/pacman"
-  if [[ ! -x $checkout/bin/omarchy-apply-pacman || ! -r $profile/pacman.conf.append || ! -r $profile/mirrorlist.append ]]; then
+  # The refresh after linking needs a runnable helper and every fragment, not
+  # just a directory with the region's name: dev refreshes edge, and leaving
+  # dev later refreshes stable or rc with this checkout's tools.
+  local profile="$checkout/default/regions/$region/pacman" fragment supported=true
+  [[ -x $checkout/bin/omarchy-apply-pacman ]] || supported=false
+  for fragment in pacman.conf.append mirrorlist-stable.prepend mirrorlist-rc.prepend mirrorlist-edge.prepend; do
+    [[ -r $profile/$fragment ]] || supported=false
+  done
+  if ! $supported; then
     fail "$checkout does not support the '$region' region, so switching would drop its package repositories. Check out a branch with default/regions/$region, or remove $region_file to use global defaults."
   fi
 }

bin/omarchy-provision-owner

@@ -16,7 +16,6 @@ set -euo pipefail
 PROVISIONING_DIR=/var/lib/omarchy/provisioning
 OMARCHY_PATH="${OMARCHY_PATH:-/usr/share/omarchy}"
 LOG_FILE=/var/log/omarchy-provision-owner.log
-REGION_MARKER=/etc/omarchy/region
 
 if (( EUID != 0 )); then
   echo "Error: omarchy-provision-owner must run as root" >&2
@@ -651,21 +650,7 @@ user_form() {
   omarchy_prompt_hostname || return $?
 
   step "Let's set your timezone..."
-  omarchy_prompt_timezone "$(region_timezone)" || return $?
-}
-
-# The zone a region profile preselects when there is no geo guess, which is
-# every offline first boot. Reads the marker omarchy-apply-pacman reads; global,
-# missing, or malformed regions offer nothing.
-region_timezone() {
-  local region=global profile
-  if [[ -r $REGION_MARKER ]]; then
-    region=$(<"$REGION_MARKER")
-  fi
-  profile="$OMARCHY_PATH/default/regions/$region/timezone"
-  if [[ $region =~ ^[a-z]{2}$ && -r $profile ]]; then
-    head -n 1 "$profile"
-  fi
+  omarchy_prompt_timezone || return $?
 }
 
 confirm_form() {