feat(lifecycle): plain-language generation diffs (#82)

nomarchy-what-changed wraps nvd into "N added, M removed, K updated"
summaries. nomarchy-rebuild / nomarchy-home print full nvd and toast
the one-liner; System › What changed? offers toast + floating report.
checks.what-changed fixtures nvd via NOMARCHY_NVD.

Verified: V2 — flake check --no-build; checks.what-changed green;
local smoke on real HM generations.

modules/home/rofi.nix

@@ -895,6 +895,20 @@ ${themeRows}
         # Nomarchy TUI Control Center.
         exec ${cfg.terminal} -e nomarchy-control-center ;;
 
+      whatchanged)
+        # Plain-language last rebuild (system + desktop nvd). Toast the
+        # one-liners; open a floating terminal for the full report when
+        # the user wants detail (same ghostty class pattern as Doctor).
+        if ! command -v nomarchy-what-changed >/dev/null 2>&1; then
+          notify-send "What changed" "nomarchy-what-changed not on PATH (lifecycle package?)."
+          exit 0
+        fi
+        summary=$(nomarchy-what-changed --summary 2>/dev/null || true)
+        [ -n "$summary" ] && notify-send -a Nomarchy "What changed" "$summary"
+        exec ghostty --class=com.nomarchy.doctor --gtk-single-instance=false \
+          -e sh -c "nomarchy-what-changed
+            printf '\nEnter to close.'; read -r _" ;;
+
       rollback)
         # Undo, one menu away (informative + rock-stable). Desktop =
         # Home Manager generations: theme/config history is already one
@@ -996,6 +1010,9 @@ ${themeRows}
           fi
           command -v nomarchy-snapshots >/dev/null 2>&1 && row "Snapshots" timeshift
           row "Rollback" edit-undo
+          # Plain-language last-rebuild summary (nvd; BACKLOG #82).
+          command -v nomarchy-what-changed >/dev/null 2>&1 \
+            && row "What changed?" view-refresh
           command -v nomarchy-doctor >/dev/null 2>&1 && row "Doctor" utilities-system-monitor
           # Firmware/LVFS updates — self-gated on fwupd (default-on, but off
           # on VMs/headless via services.fwupd.enable=false), like Printers.
@@ -1024,6 +1041,7 @@ ${themeRows}
           *"Auto-commit"*)    exec "$0" autocommit ;;
           *Snapshots*)        exec "$0" snapshot ;;
           *Rollback*)         exec "$0" rollback ;;
+          *"What changed"*)   exec "$0" whatchanged ;;
           *Doctor*)           exec "$0" doctor ;;
           *Firmware*)         exec "$0" firmware ;;
           *Fingerprint*)      exec "$0" fingerprint ;;
@@ -1134,7 +1152,7 @@ ${themeRows}
         esac ;;
 
       *)
-        echo "usage: nomarchy-menu [lookfeel|tools|system|power|power-profile|powermgmt|batterylimit|theme|clipboard|calc|files|emoji|web|network|bluetooth|audio|display|display-profile|printers|capture|colorpicker|keybinds|ask|dnd|nightlight|autotimezone|autocommit|vpn|snapshot|doctor|firmware|fingerprint|controlcenter|rollback]" >&2
+        echo "usage: nomarchy-menu [lookfeel|tools|system|power|power-profile|powermgmt|batterylimit|theme|clipboard|calc|files|emoji|web|network|bluetooth|audio|display|display-profile|printers|capture|colorpicker|keybinds|ask|dnd|nightlight|autotimezone|autocommit|vpn|snapshot|doctor|firmware|fingerprint|controlcenter|rollback|whatchanged]" >&2
         exit 64 ;;
     esac
   '';