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-plymouth-set

@@ -42,7 +42,7 @@ theme_dir="/usr/share/plymouth/themes/omarchy"
 staging_dir=$(mktemp -d)
 trap 'rm -rf "$staging_dir"' EXIT
 
-find ~/.local/share/omarchy/default/plymouth -maxdepth 1 -type f -exec cp -t "$staging_dir/" {} +
+find $OMARCHY_PATH/default/plymouth -maxdepth 1 -type f -exec cp -t "$staging_dir/" {} +
 cp "$logo_path" "$staging_dir/logo.png"
 
 sed -i \
@@ -65,7 +65,7 @@ fi
 
 # Sync the SDDM login screen with the same colors and logo.
 sddm_dir="/usr/share/sddm/themes/omarchy"
-sddm_template="$HOME/.local/share/omarchy/default/sddm/omarchy/Main.qml"
+sddm_template="$OMARCHY_PATH/default/sddm/omarchy/Main.qml"
 
 sed \
   -e "s/#1a1b26/#$bg_hex/g" \