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).

templates/downstream/home.nix

@@ -86,7 +86,7 @@
     mpv                 # media player
     amberol             # music player (local library; streaming → spotify below)
     pwvucontrol         # PipeWire volume mixer (right-click the Waybar volume)
-    calcurse            # TUI calendar — click the Waybar clock to open it
+    # calcurse ships with the Waybar clock (modules/home/waybar.nix)
 
     # ── More apps — uncomment to add ─────────────────────────────────
     # Web browsers