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.

themes/executive-slate/rofi.rasi

@@ -65,7 +65,7 @@ listview {
     columns: 1;
     lines: 8;
     dynamic: true;
-    scrollbar: false;
+    scrollbar: true;
     spacing: 4px;
     padding: 4px 0px 0px 0px;
 }
@@ -116,4 +116,10 @@ textbox {
     padding: 9px 14px;
 }
 
-scrollbar { width: 0px; }
+scrollbar {
+    width: 4px;
+    handle-width: 4px;
+    handle-color: @accent;
+    background-color: @surface;
+    border: 0px;
+}