feat: close #54 V2 install safety, #33 rofi scrollbar, #43 MOTD tip

#54: permanent checks.installer-safety; test-install-safety harness with
offline compose-fail, LUKS-signature disk warn, and HM-hint FORCE paths.
#33: enable themed rofi scrollbars (generated + all whole-swap .rasi).
#43: MOTD + first-boot tip for System › Firmware (V3 LVFS stays hw-queue).

V2: compose-fail/disk-warn/hm-hint logs green offline; theme-shot
boreal+summer-night menus OK. V0 flake/installer-safety.

modules/home/rofi.nix

@@ -1128,11 +1128,21 @@ in
             lines = 8;
             columns = 1;
             dynamic = true;
-            scrollbar = false;
+            # Scrollbar only draws when lines < rows (rofi self-hides on
+            # short menus). Overflow hint for long lists / launcher grids.
+            scrollbar = true;
             spacing = px 4; # a little air so the rounded zebra rows separate
             padding = mkLiteral "8px 0px 0px 0px";
           };
 
+          "scrollbar" = {
+            width = px 4;
+            handle-width = px 4;
+            handle-color = mkLiteral "@accent";
+            background-color = mkLiteral "@surface";
+            border = px 0;
+          };
+
           # Rounded, roomy rows with subtle zebra striping: alternate rows
           # lift to @surface, the selected row to @accent. normal/alternate/
           # selected are rofi's row parities (the `.normal` suffix is the

modules/nixos/default.nix

@@ -57,6 +57,7 @@ in
         home-update                         apply home/theme changes (no sudo)
         nomarchy-theme-sync apply <theme>   switch the whole palette
         SUPER+?                             keybindings cheatsheet
+        SUPER+M → System › Firmware         check LVFS firmware updates (fwupd)
     '';
 
     # Unfree allowed distro-wide: pragmatic-desktop territory (vendor