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).

modules/nixos/default.nix

@@ -69,7 +69,11 @@ in
     # GPU/wifi drivers, firmware, fonts, …). The custom nixpkgs-config
     # type can't carry a nested mkDefault; disagree with
     # `nixpkgs.config = lib.mkForce { allowUnfree = false; }`.
+    # `NIXPKGS_ALLOW_UNFREE` covers CLI `nix-shell` / `nix shell` /
+    # `nix run` (those ignore the system `nixpkgs.config`); pure flake
+    # eval still needs `--impure` when the env var is the only gate.
     nixpkgs.config.allowUnfree = true;
+    environment.variables.NIXPKGS_ALLOW_UNFREE = "1";
 
     # ── One keyboard layout everywhere, incl. the LUKS prompt ────────
     # services.xserver.xkb.layout is the single source of truth for the