fix(deploy): console=tty0 was being dropped on the Pi 5

raspberry-pi-5.nix set `boot.kernelParams = lib.mkDefault [ "console=tty0" ]`
to keep the serial console off the GPIO UART so a validator can own it. It
never took effect: kernelParams is list-merged, and only definitions at the
highest priority survive — nixpkgs defines loglevel/lsm at normal priority,
so the mkDefault list was discarded wholesale. Effective params on
rpi5-installed were `[ "loglevel=4" "lsm=landlock,yama,bpf" ]`, no console=
at all, which makes the kernel fall back to the device tree's stdout-path:
that same UART.

Drop the mkDefault so the entry merges. Verified by evaluating
config.boot.kernelParams before/after.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013A6683cCHnQxFUosx1krY4

deploy/nixos/hardware/raspberry-pi-5.nix

@@ -30,7 +30,12 @@
   # Primary UART (GPIO 14/15) available for a GPIO-wired validator. Keep the
   # serial console OFF it so the validator owns the line — mirrors upboard.nix
   # keeping ttyS4 free for the dispenser. USB-serial adapters are unaffected.
-  boot.kernelParams = lib.mkDefault [ "console=tty0" ];
+  #
+  # Not mkDefault: kernelParams is list-merged, and only definitions at the
+  # highest priority survive. nixpkgs sets loglevel/lsm at normal priority, so
+  # a mkDefault list here is dropped entirely — and with no console= at all
+  # the kernel falls back to the device tree's stdout-path, i.e. this UART.
+  boot.kernelParams = [ "console=tty0" ];
 
   # X uses the Pi GPU's kernel modesetting driver (vc4/v3d KMS from
   # nixos-hardware). Electron renders through it as on the UP Board.