Normalize hard-coded ~/.local/share/omarchy refs to $OMARCHY_PATH

The package-installed paths live at /usr/share/omarchy; the script-install
paths live at ~/.local/share/omarchy. $OMARCHY_PATH is set by install.sh
during the install flow and by /etc/profile.d/omarchy.sh in package mode.
Scripts that hard-code the script-install path don't honour that and will
misbehave once shipped to /usr/bin.

16 files migrated via sed s|~/\.local/share/omarchy|$OMARCHY_PATH|g
and s|$HOME/\.local/share/omarchy|$OMARCHY_PATH|g:

bin/:
- omarchy-plymouth-{preview,reset,set}
- omarchy-refresh-{limine,plymouth}
- omarchy-reinstall-configs
- omarchy-show-logo
- omarchy-games-retro-install
- omarchy-install-gaming-battlenet

install/:
- config/branding.sh
- packaging/{fonts,icons}.sh
- post-install/{finished,pacman}.sh
- preflight/{migrations,pacman}.sh

Deliberately NOT migrated:
- bin/omarchy-dev-add-migration: uses 'cd ~/.local/share/omarchy' to
  resolve a git repo for 'git log'. The packaged binary doesn't have a
  git repo to read; this command only makes sense in dev mode where
  the home path is the right one.
- bin/omarchy-install-browser:69: writes a string into a chromium
  config file that chromium itself interprets; not a bash-resolved path.
- install/helpers/errors.sh:125: the boot.sh-style relaunch behaviour
  needs a separate redesign.

bin/omarchy-games-retro-install

@@ -55,7 +55,7 @@ icon_dir="$desktop_dir/icons"
 icon_path="$icon_dir/Retro Gaming.png"
 
 mkdir -p "$desktop_dir" "$icon_dir"
-[[ -f $icon_path ]] || cp "$HOME/.local/share/omarchy/applications/icons/Retro Gaming.png" "$icon_path"
+[[ -f $icon_path ]] || cp "$OMARCHY_PATH/applications/icons/Retro Gaming.png" "$icon_path"
 
 cat >"$desktop_file" <<EOF
 [Desktop Entry]