fix(autoswitch): WorkspacesChanged output-set diff; unit paths; deploy symlinks

- niri 26.04 has no hotplug event: OutputConfigChanged is only an ACK
  (niri-ipc). Watch WorkspacesChanged, diff sorted output set, apply on
  change. Proven live: eDP-1 off/on -> 3 output-set transitions, each
  matched + applied + reloaded.
- unit: %h/.local/bin/desk-autoswitch.sh, quoted Environment, drop
  User/Group (user unit); add desk-autoswitch.sh bin symlink
- desk.sh: silence validate/load-config/notify stdout
- deploy.sh: deploy repo symlinks (find -type l), so .local/bin links land
- docs: event semantics corrected (displays diagram, log)

dotfiles/zz-blankpad/.local/bin/desk-autoswitch.sh

@@ -0,0 +1 @@
+../../../../scripts/desk-autoswitch.sh