Phase 18: internet realtime collaboration (GM-authoritative) + server

- Shared Zod wire protocol (src/lib/sync/messages.ts): hosted/joined/snapshot/
  mapImage/error; player-safe projections only (enemy HP masked on the GM before
  broadcast via src/lib/combat/playerProjection.ts).
- wsSync adapter (src/lib/sync/wsSync.ts) behind the existing SyncAdapter seam:
  GM hostSession + debounced snapshot broadcast (useSessionBroadcaster), player
  joinSession into an ephemeral playerSessionStore, exponential-backoff reconnect
  with seamless room resume (GM secret). localSync remains the offline default.
- buildSnapshot (src/lib/sync/snapshot.ts) reuses the same projection as the local
  /play view, guaranteeing parity. Player view refactored into shared PlayerBoards;
  /play?room=CODE = networked read-only mode.
- SessionControl in the header: Host (optional password) → shareable room code/link.
- Server (server/): Fastify + @fastify/websocket + @fastify/static, in-memory
  GM-authoritative rooms (crypto room id/secret hashed, optional join password,
  TTL sweep, players strictly read-only), origin allowlist, per-frame size cap +
  rate limit, Zod validation. esbuild bundle (server/build.mjs), tsconfig.server.json.
- Dockerfile (multi-stage) + deploy/ttrpg.compose.yml (own project on external
  'proxy' net, Traefik labels for ttrpg.briggen.dev, non-root, no-new-privileges).
  CSP connect-src now allows same-origin wss:.

Tests: protocol round-trip, room hub (auth/password/resume/TTL/read-only), enemy
masking, Fastify+ws integration (host→join→snapshot, player push rejected), and a
two-context Playwright realtime spec (separate config) — GM hosts, player device
sees live combat with masked enemy HP.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/stores/playerSessionStore.ts

@@ -0,0 +1,20 @@
+import { create } from 'zustand';
+import type { Snapshot } from '@/lib/sync/messages';
+
+interface PlayerSessionState {
+  snapshot: Snapshot | null;
+  /** map image data URLs keyed by map id, cached so they don't re-stream */
+  images: Record<string, string>;
+  setSnapshot: (s: Snapshot) => void;
+  setImage: (id: string, dataUrl: string) => void;
+  reset: () => void;
+}
+
+/** Ephemeral store holding what a joined player currently sees (never persisted). */
+export const usePlayerSessionStore = create<PlayerSessionState>()((set) => ({
+  snapshot: null,
+  images: {},
+  setSnapshot: (snapshot) => set({ snapshot }),
+  setImage: (id, dataUrl) => set((s) => ({ images: { ...s.images, [id]: dataUrl } })),
+  reset: () => set({ snapshot: null, images: {} }),
+}));