fix(desktop): unfree CLI default, bar icon spacing, unified clock

Hardware findings on Latitude: nix-shell blocked unfree; whole-swap
bars collided icon+percentage; clock needed calcurse + one module.

- Export NIXPKGS_ALLOW_UNFREE=1 + ~/.config/nixpkgs/config.nix
- Mono Nerd face + trailing spaces on battery/volume icons (all bars)
- Single clock `HH:MM · Day DD Mon`; calcurse ships with waybar
- V3 queue entries for laptop re-check

Verification: V0 — nix flake check --no-build green; V2/V3 pending on
session (user-visible bar + CLI unfree).

themes/summer-day/waybar.css

@@ -48,7 +48,6 @@ window#waybar {
 #custom-recording,
 #idle_inhibitor,
 #clock,
-#clock-date,
 #workspaces,
 #pulseaudio,
 #custom-powerprofile,