kaintuck: shared-market server deploy + connection/gossip UI

#54 in Riparion/riparion-retro — merged 2026-06-15

Ships kaintuck multiplayer end-to-end.

Server deploy — kaintuck-server runs as its own Docker stack beside the CMS (it only hosts static bundles), fronted by NPM at a dedicated wss subdomain. Adds Dockerfile.kaintuck-server, docker-compose.kaintuck-server.yml (joins the host reverse-proxy net via PROXY_NETWORK), and deploy-server/inprod-server recipes.

Client UI — a slim SharedMarket bar shows the connection state (● shared market) and a live feed of gossip about the other traders. Renders nothing offline, so single-player is unchanged. Bumps kaintuck 0.1.24 → 0.1.25.

Verified: headless browser against the live QA/prod apps connects the WebSocket and renders the indicator + gossip.

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