feat(deploy): local chess.local instance for VDJ-RIG

A second, LAN-only deploy alongside the CT 690 / chess.sethpc.xyz
instance. Runs on VDJ-RIG as a persistent systemd daemon, served on
port 80 and reachable at http://chess.local via an mDNS alias.

- blind-chess-local.service: server unit; binds port 80 as the
  non-root blindchess user via CAP_NET_BIND_SERVICE.
- chess-mdns-alias{,.service}: publishes the chess.local mDNS name
  with avahi-publish -a -R (-R skips the reverse PTR, which would
  otherwise collide with the host's own <hostname>.local record).
- install-local.sh: idempotent root-side installer (Node 22 via
  NodeSource, avahi-utils, blindchess user, /opt/blind-chess, units).
- CLAUDE.md: documents the local instance under Operations.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

deploy/chess-mdns-alias.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Publish chess.local mDNS alias for the blind_chess local deploy
+Requires=avahi-daemon.service
+After=avahi-daemon.service network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=/usr/local/bin/chess-mdns-alias
+Restart=always
+RestartSec=5s
+
+[Install]
+WantedBy=multi-user.target