fix(theme): set default to summer-night and fix scripts on live ISO

- Update lib/state-schema.nix to default both home and system themes to 'summer-night'.
- Fix 'nomarchy-theme-list' and 'nomarchy-theme-set-templates' to resolve themes and templates from '~/.local/share/nomarchy' instead of the obsolete '$NOMARCHY_PATH' (fixing failures on Live ISO).
- Update 'nomarchy-welcome' to properly convert Title Case theme display names back to kebab-case identifiers and add input validation to prevent crashes.
- Fix installer impermanence symlink by using a relative path ('../persist/etc/nixos'), ensuring it resolves during 'nixos-install' both inside and outside the chroot.
- Deploy '~/.XCompose' symlink via Home Manager and add 'nomarchy-restart-xcompose' to the menu.
- Relocate 'Nomarchy.ttf' to 'core/branding/' and move user-level scripts ('pkg-add', 'pkg-remove', 'env-update', 'preflight-migration') to 'features/scripts/utils/' to align with the distro architecture.
- Remove obsolete '$NOMARCHY_PATH' exports and redundant 'bashrc' template.
- Export theme templates via 'xdg.dataFile' for script accessibility.

features/scripts/utils/nomarchy-welcome

@@ -28,16 +28,25 @@ echo ""
 
 # 1. Select initial theme
 echo "Step 1: Choose your starting theme"
-nomarchy-theme-set "$(nomarchy-theme-list | gum filter --placeholder 'Select a theme...')" --no-update
+SELECTED_THEME="$(nomarchy-theme-list | gum filter --placeholder 'Select a theme...')"
+if [[ -n "$SELECTED_THEME" ]]; then
+    THEME_ID=$(echo "$SELECTED_THEME" | tr '[:upper:]' '[:lower:]' | tr ' ' '-')
+    nomarchy-theme-set "$THEME_ID" --no-update
+fi
 
 # 2. Select initial font
 echo "Step 2: Choose your preferred font"
-nomarchy-font-set "$(nomarchy-font-list | gum filter --placeholder 'Select a font...')" --no-update
+SELECTED_FONT="$(nomarchy-font-list | gum filter --placeholder 'Select a font...')"
+if [[ -n "$SELECTED_FONT" ]]; then
+    nomarchy-font-set "$SELECTED_FONT" --no-update
+fi
 
 # 3. Select panel position
 echo "Step 3: Choose your preferred panel position"
 POSITION=$(gum choose "top" "bottom")
-nomarchy-state-write panelPosition "$POSITION"
+if [[ -n "$POSITION" ]]; then
+    nomarchy-state-write panelPosition "$POSITION"
+fi
 
 # Skip system-modifying steps in the Live ISO environment
 if [[ "$USER" == "nixos" ]]; then