perf(deploy): trim systemPackages to kiosk essentials

Every entry here ships to each ATM and eats the eMMC headroom the
nightly nixos-rebuild needs, which is tight enough already that GC runs
at 03:30 purely to clear room for the 04:00 upgrade.

Out: git, at 70MB, since nixos-rebuild fetches the flake with its own
git-minimal that unit-nixos-upgrade.service keeps in the closure, so
auto-upgrade is unaffected. nodejs_22, at 94MB, which nothing runs: the
app is Electron and embeds its own node, and fund-atm references
pkgs-unstable.nodejs by store path. wget, which curl covers. And vim,
replaced by nano.

Keeping an editor at all is deliberate. Field edits to
/var/lib/bitspire/.env happen over ssh, and nano costs a few MB where
vim costs 43. minicom and screen stay for the same reason: the validator
and dispenser sit on ttyJ5 and ttyJ7, those two are how a serial fault
gets diagnosed, and they cost about 2MB between them.

With the two preceding commits the sintra-installed closure goes from
5144MB to 4604MB across 131 fewer store paths.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

deploy/nixos/configuration.nix

@@ -111,29 +111,37 @@
   };
 
   # System packages
+  #
+  # Kept deliberately thin — this is a kiosk, and every entry here is closure
+  # that ships to each ATM and eats eMMC headroom the nightly rebuild needs.
+  # Deliberately absent (see #70 sizing):
+  #   git     70MB. nixos-rebuild fetches the flake with its OWN git-minimal,
+  #           which stays in the closure via unit-nixos-upgrade.service, so
+  #           auto-upgrade is unaffected.
+  #   vim     43MB. Replaced by nano — an on-box editor is worth a few MB for
+  #           field edits to /var/lib/bitspire/.env, vim's bulk is not.
+  #   nodejs_22  94MB. Nothing runs it: the app is Electron (which embeds its
+  #           own node) and fund-atm already pins pkgs-unstable.nodejs itself.
+  #   wget    curl covers it.
   environment.systemPackages = with pkgs; [
     # System utilities
     htop
-    vim
-    git
+    nano
     curl
-    wget
 
     # Hardware debugging
     usbutils
     pciutils
     lsof
 
-    # Serial port tools
+    # Serial port tools (validator/dispenser live on ttyJ5/ttyJ7 — these are
+    # how a field fault gets diagnosed, and they cost ~2MB between them)
     minicom
     screen
 
     # For the Electron app
     pkgs-unstable.electron
 
-    # Node.js for the application
-    pkgs-unstable.nodejs_22
-
     # Camera support. v4l-utils' default build drags in the whole Qt6 stack
     # for its qv4l2 GUI (~0.5GB) — we only ever use the v4l2-ctl CLI, so drop
     # the GUI.