Add visual smoothing for snake game and systemd deployment

CSS animations for smoother 60fps feel despite 7Hz game ticks:
- 130ms transitions on cell background/box-shadow
- Head pop-in animation on direction changes
- Food pulse animation
- Smooth death state fade with grayscale

Per-snake colored glow on head cells.

Make server port configurable via PORT env var (default 8080).

Add deploy/ with systemd service and scripts:
- setup.sh: create games user, /opt/c4, install unit
- deploy.sh: build and install binary, restart service
- package.sh: cross-compile, tarball, base64 split for transfer
- reassemble.sh: decode and extract on target server

deploy/setup.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+# One-time setup: create the games user, install directory, and systemd unit.
+# Run as root (or with sudo).
+set -euo pipefail
+
+if [[ $EUID -ne 0 ]]; then
+  echo "Run as root: sudo $0" >&2
+  exit 1
+fi
+
+# Create system user if it doesn't exist
+if ! id -u games &>/dev/null; then
+  useradd --system --shell /usr/sbin/nologin --home-dir /opt/c4 --create-home games
+  echo "Created system user: games"
+else
+  echo "User 'games' already exists"
+fi
+
+# Ensure install directory exists with correct ownership
+install -d -o games -g games -m 755 /opt/c4
+install -d -o games -g games -m 755 /opt/c4/data
+
+# Install systemd unit
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+cp "$SCRIPT_DIR/c4.service" /etc/systemd/system/c4.service
+systemctl daemon-reload
+systemctl enable c4.service
+
+echo "Setup complete. Run deploy.sh to build and start the service."