feat(web): add WebSocket client and context infrastructure

- WsClient class: connect/disconnect/send/on/off/isConnected/clearCallbacks
- connect() derives wss:// from https:// automatically, returns Promise<void>
- on/off typed with Extract<WsServerMessage, { type: T }> for precise
  callback narrowing, callbacks stored as Map<string, Set<fn>>
- ws-context.ts: WsContextValue type + WsContext definition
- ws-provider.tsx: WsProvider with module-level wsClient singleton,
  owns connection lifecycle (connect/disconnect/isConnected state)
- ws-hooks.ts: useWsClient, useWsConnected, useWsConnect, useWsDisconnect

apps/web/src/lib/ws-hooks.ts

@@ -0,0 +1,35 @@
+import { useContext } from "react";
+import { WsContext } from "./ws-context.js";
+import type { WsClient } from "./ws-client.js";
+
+export const useWsClient = (): WsClient => {
+  const ctx = useContext(WsContext);
+  if (!ctx) {
+    throw new Error("useWsClient must be used within a WsProvider");
+  }
+  return ctx.client;
+};
+
+export const useWsConnected = (): boolean => {
+  const ctx = useContext(WsContext);
+  if (!ctx) {
+    throw new Error("useWsConnected must be used within a WsProvider");
+  }
+  return ctx.isConnected;
+};
+
+export const useWsConnect = (): ((url: string) => Promise<void>) => {
+  const ctx = useContext(WsContext);
+  if (!ctx) {
+    throw new Error("useWsConnect must be used within a WsProvider");
+  }
+  return ctx.connect;
+};
+
+export const useWsDisconnect = (): (() => void) => {
+  const ctx = useContext(WsContext);
+  if (!ctx) {
+    throw new Error("useWsDisconnect must be used within a WsProvider");
+  }
+  return ctx.disconnect;
+};