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/reassemble.sh

@@ -0,0 +1,96 @@
+#!/usr/bin/env bash
+# Reassembles base64 chunks and extracts the c4 deployment tarball.
+# Expects chunk files in the current directory.
+set -euo pipefail
+
+cd "$HOME"
+
+echo "=== C4 Deployment Reassembler ==="
+echo "Working directory: $HOME"
+echo ""
+
+#==============================================================================
+# Find and validate chunk files
+#==============================================================================
+echo "--- Finding chunk files ---"
+
+CHUNKS=($(ls -1 c4-deploy-*_b64_part*.txt 2>/dev/null | sort))
+
+if [[ ${#CHUNKS[@]} -eq 0 ]]; then
+  echo "ERROR: No chunk files found matching c4-deploy-*_b64_part*.txt"
+  exit 1
+fi
+
+echo "Found ${#CHUNKS[@]} chunks:"
+for chunk in "${CHUNKS[@]}"; do
+  echo "  - $chunk ($(du -h "$chunk" | cut -f1))"
+done
+
+#==============================================================================
+# Reassemble and decode
+#==============================================================================
+echo ""
+echo "--- Reassembling chunks ---"
+
+TIMESTAMP=$(echo "${CHUNKS[0]}" | sed -E 's/c4-deploy-([0-9]+-[0-9]+)_b64_part.*/\1/')
+TARBALL="c4-deploy-${TIMESTAMP}.tar.gz"
+COMBINED="combined_b64.txt"
+
+echo "Concatenating chunks..."
+cat "${CHUNKS[@]}" > "$COMBINED"
+echo "  -> Created $COMBINED ($(du -h "$COMBINED" | cut -f1))"
+
+echo "Decoding base64..."
+base64 -d "$COMBINED" > "$TARBALL"
+echo "  -> Created $TARBALL ($(du -h "$TARBALL" | cut -f1))"
+
+echo "Verifying tarball..."
+if tar -tzf "$TARBALL" > /dev/null 2>&1; then
+  echo "  -> Tarball is valid"
+else
+  echo "ERROR: Tarball verification failed"
+  exit 1
+fi
+
+#==============================================================================
+# Archive existing source
+#==============================================================================
+echo ""
+echo "--- Archiving existing source ---"
+
+if [[ -d c4 ]]; then
+  rm -rf c4.bak
+  mv c4 c4.bak
+  echo "  -> Moved c4 -> c4.bak"
+else
+  echo "  -> No existing c4 directory"
+fi
+
+#==============================================================================
+# Extract
+#==============================================================================
+echo ""
+echo "--- Extracting tarball ---"
+
+tar -xzf "$TARBALL"
+echo "  -> Extracted to ~/c4"
+
+#==============================================================================
+# Cleanup
+#==============================================================================
+echo ""
+echo "--- Cleaning up ---"
+
+rm -f "$COMBINED" "$TARBALL" "${CHUNKS[@]}"
+echo "  -> Removed chunks, combined base64, and tarball"
+
+#==============================================================================
+# Next steps
+#==============================================================================
+echo ""
+echo "=== Reassembly Complete ==="
+echo ""
+echo "Next steps:"
+echo "  cd ~/c4"
+echo "  sudo ./deploy/setup.sh   # first time only"
+echo "  sudo ./deploy/deploy.sh"