fix: TUI mit drei Backends (gum/whiptail/basic) + gum auto-install auf frischen Systemen

- tui.sh: komplett überarbeitet mit _strip_format() für basic mode
- whiptail als mittleres Fallback-Backend hinzugefügt
- Alle #{bold}/#{normal}-Markups entfernt, saubere ANSI-API (tui_info/tui_bold/...)
- install.sh: detect_environment() installiert gum vor allen Prompts
- Kein seq-Dependency mehr (printf -v statt seq)
- packages.sh/preflight.sh/homelab.sh/optional.sh auf neue TUI-API migriert

modules/optional/install.sh

@@ -14,14 +14,13 @@ module_prereqs() {
 module_main() {
   log_section "Optional Software Selection"
 
-  tui_format "#{bold}Select software to install:#{normal}"
-  tui_format "Use space to select, enter to confirm."
-  tui_format ""
+  tui_bold "Select optional software to install:"
+  tui_info "Use space (gum) or enter indices (basic) to select."
+  printf '\n'
 
   local choices
   choices="$(
-    gum choose --no-limit \
-      --header "Select optional packages (space to toggle, enter to confirm)" \
+    tui_multiselect "Software Selection" \
       "Obsidian" \
       "Neovim" \
       "Visual Studio Code" \
@@ -31,7 +30,7 @@ module_main() {
       "VLC" \
       "PipeWire Tools" \
       "Docker" \
-      "Blender" 2>&1
+      "Blender"
   )"
 
   if [[ -z "$choices" ]]; then