feat(live): #57 Install Nomarchy desktop entry + Tools row

Always-visible install surface on the live ISO: xdg.desktopEntries
(Terminal=true) plus Tools › Install Nomarchy (self-gated on
nomarchy-install on PATH). Welcome toast mentions the app. Close #57.

Verified: V1 (live eval + HM menu rebuild). V2 pending: ISO smoke.

modules/home/rofi.nix

@@ -750,6 +750,10 @@ ${themeRows}
         # Tools submenu — utilities you invoke. Each leaf is also reachable
         # directly (SUPER+CTRL+<mnemonic>); this just keeps the root short.
         choice=$( {
+          # Live ISO only: nomarchy-install is systemPackages on the live
+          # host (BACKLOG #57). Installed systems never ship the package.
+          command -v nomarchy-install >/dev/null 2>&1 \
+            && row "Install Nomarchy" system-software-install
           row "Calculator${menuHint "calc"}" accessories-calculator
           row "Clipboard${menuHint "clipboard"}"  edit-paste
           row "Emoji${menuHint "emoji"}"      face-smile-big
@@ -762,6 +766,11 @@ ${themeRows}
         } | rofi -dmenu -show-icons -markup-rows -p Tools) || exit 0
         case "$choice" in
           "$BACK")     exec "$0" ;;
+          *"Install Nomarchy"*)
+            command -v nomarchy-install >/dev/null 2>&1 \
+              && exec ${cfg.terminal} -e nomarchy-install
+            notify-send "Install" "nomarchy-install is not on PATH (live ISO only)."
+            exit 0 ;;
           *Calc*)      exec "$0" calc ;;
           *Clipboard*) exec "$0" clipboard ;;
           *Emoji*)     exec "$0" emoji ;;