Installer: cleanup of restart-check, --clone and the uninstall changes

- uninstall: nix-installer's copy outside /nix is made and run as root
  (a user-writable copy run by sudo could be swapped); README uninstall
  paragraph shortened to one account of what happens when Nix stays.
- session.nix: the restart-check activation after steamFrameUserServices,
  so the latter's comment is above it again.
- install.sh: a duplicate `local` in port_listening; comments.
- docs/cleanup.md: the installer internals of --clone (how an existing
  clone is recognised, which git) and restart-check (what it compares,
  test overrides); README keeps the usage.
- README install paragraph: shorter list of the dashboard patches.

modules/session.nix

@@ -98,12 +98,6 @@ in {
 
   # In a subshell: the outer session's environment must not leak into
   # activation steps that run later.
-  # Read-only; a warning, never a failed switch.
-  config.home.activation.steamFrameRestartCheck = lib.hm.dag.entryAfter [ "steamFrameUserServices" ] ''
-    STEAM_FRAME_NIX_RUNTIME_DIR=${lib.escapeShellArg cfg.runtimeDir} XDG_CONFIG_HOME=${lib.escapeShellArg config.xdg.configHome} \
-      ${lib.getExe restartCheck} || true
-  '';
-
   config.home.activation.steamFrameUserServices = lib.hm.dag.entryAfter [ "reloadSystemd" ] (''
     (
     export XDG_RUNTIME_DIR=${lib.escapeShellArg cfg.runtimeDir} DBUS_SESSION_BUS_ADDRESS=${lib.escapeShellArg cfg.bus}
@@ -121,4 +115,10 @@ in {
   '' + ''
     )
   '');
+
+  # Read-only; a warning, never a failed switch.
+  config.home.activation.steamFrameRestartCheck = lib.hm.dag.entryAfter [ "steamFrameUserServices" ] ''
+    STEAM_FRAME_NIX_RUNTIME_DIR=${lib.escapeShellArg cfg.runtimeDir} XDG_CONFIG_HOME=${lib.escapeShellArg config.xdg.configHome} \
+      ${lib.getExe restartCheck} || true
+  '';
 }