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/deploy.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Deploy the c4 binary to /opt/c4, then restart the service.
+# Works from the repo (builds first) or from an extracted tarball (pre-built binary).
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+INSTALL_DIR="/opt/c4"
+BINARY="$ROOT_DIR/c4"
+
+# If Go is available and we have source, build fresh
+if [[ -f "$ROOT_DIR/go.mod" ]] && command -v go &>/dev/null; then
+  echo "Building CSS..."
+  (cd "$ROOT_DIR" && go tool gotailwind -i assets/css/input.css -o assets/css/output.css --minify)
+
+  echo "Building binary..."
+  (cd "$ROOT_DIR" && CGO_ENABLED=0 go build -o c4 .)
+fi
+
+if [[ ! -f "$BINARY" ]]; then
+  echo "ERROR: Binary not found at $BINARY" >&2
+  exit 1
+fi
+
+echo "Installing to $INSTALL_DIR..."
+install -o games -g games -m 755 "$BINARY" "$INSTALL_DIR/c4"
+
+echo "Restarting service..."
+systemctl restart c4.service
+
+echo "Done. Status:"
+systemctl status c4.service --no-pager