Make setup ISO-only

Remove legacy online installer entrypoints, collapse migrations for 4.0, and move setup responsibilities into target-side system, hardware, and user commands.

install/user/theme.sh

@@ -0,0 +1,14 @@
+# Setup user theme folder
+mkdir -p ~/.config/omarchy/themes
+
+if [[ ${OMARCHY_SETUP_CONTEXT:-runtime} == "iso-chroot" ]]; then
+  OMARCHY_THEME_HEADLESS=1 omarchy-theme-set "Tokyo Night"
+else
+  omarchy-theme-set "Tokyo Night"
+fi
+
+rm -rf ~/.config/chromium/SingletonLock
+omarchy-theme-set-pi --activate
+
+mkdir -p ~/.config/btop/themes
+ln -snf ~/.config/omarchy/current/theme/btop.theme ~/.config/btop/themes/current.theme