feat(menu): group keybinds cheatsheet Window/Workspace/Menu/Media (#108)

Every bind in keybinds.nix carries a group; SUPER+? renders section
headers. checks.keybinds-cheatsheet asserts all groups are valid and
every description appears in the sheet (same source as Hyprland binds).

Verified: V0 flake check; built cheatsheet shows ── Window ── / etc.

modules/home/rofi.nix

@@ -133,17 +133,37 @@ let
         # renders "SHIFT + /". `?` IS Shift+/, so collapse that back to the
         # single documented glyph — the cheatsheet reads "SUPER + ?".
     in lib.replaceStrings [ "SHIFT + /" ] [ "?" ] (prefix + key);
-  cheatRows =
-    map (b: padRight 22 (prettyKeys b) + b.desc) (keybinds.binds
+  # Grouped cheatsheet (#108): Window → Workspace → Menu → Media.
+  # Section headers are non-selectable chrome (rofi still shows them as rows;
+  # Enter is a no-op either way). Order matches the group enum.
+  cheatGroupOrder = [ "Window" "Workspace" "Menu" "Media" ];
+  cheatBindRows =
+    map (b: {
+      inherit (b) group desc;
+      keys = prettyKeys b;
+    }) (keybinds.binds
       ++ lib.optionals (lib.hasInfix "," cfg.keyboard.layout)
          keybinds.multiLayoutBinds)
     # Launch-or-focus binds (nomarchy.launchOrFocus, generated in
     # hyprland.nix) — same renderer, so they land in the cheatsheet too.
-    ++ map (e: padRight 22 (prettyKeys e)
-               + (if e.desc != "" then e.desc
-                  else "Focus or launch ${if e.command == "" then lib.toLower e.class else e.command}"))
-         cfg.launchOrFocus
-    ++ map (e: padRight 22 e.keys + e.desc) keybinds.extra;
+    ++ map (e: {
+      group = "Menu";
+      keys = prettyKeys e;
+      desc = if e.desc != "" then e.desc
+             else "Focus or launch ${if e.command == "" then lib.toLower e.class else e.command}";
+    }) cfg.launchOrFocus
+    ++ map (e: {
+      group = e.group or "Menu";
+      keys = e.keys;
+      inherit (e) desc;
+    }) keybinds.extra;
+  cheatRowsFor = g:
+    let rows = lib.filter (r: r.group == g) cheatBindRows;
+    in lib.optionals (rows != [ ]) (
+      [ ("── " + g + " ──") ]
+      ++ map (r: padRight 22 r.keys + r.desc) rows
+    );
+  cheatRows = lib.concatLists (map cheatRowsFor cheatGroupOrder);
   cheatsheetFile = pkgs.writeText "nomarchy-keybinds.txt"
     (lib.concatStringsSep "\n" cheatRows + "\n");