modules/cleanup.nix: orphan cleanup on every switch

Every module imports cleanup.nix (also exported as
homeManagerModules.cleanup), which
- puts steam-frame-nix-cleanup (install.sh cleanup) on PATH;
- runs `cleanup --orphans --quiet` after linkGeneration on every switch,
  keeping what the configuration still uses (steamFrame.cleanup.keep, set
  by the modules: debugger while steamvrDebugger is on, the Firefox desktop
  profile's user.js while its fix applies); in a dry run it runs with
  --dry-run;
- runs `cleanup --all` instead when Home Manager's `uninstall = true;` is
  set (the manual uninstall route);
- removes links of older versions at paths Home Manager is about to own
  before checkLinkTargets (steamFrame.cleanup.migrateLinks), which would
  count as collisions otherwise.

install.sh cleanup gains --quiet (only actions, deferrals and warnings;
the header only when something is printed). The Jellyfin module's own
removal of the old shim copy goes: cleanup does it.

modules/launcher-menu.nix

@@ -27,6 +27,7 @@ let
   };
 in {
   imports = [
+    ./cleanup.nix
     ./steam-ui-patches.nix
     (lib.mkRenamedOptionModule
       [ "steamFrame" "launcherMenu" "launchDebounce" ]