[saadkhantareen]

Summary

The socket.io-client package ships a standalone ESM bundle (dist/socket.io.esm.min.js), but there is no subpath export for it, so users who want to import the client without a bundler (for example with Deno, or directly in the browser) have to copy the bundle locally or use a CDN URL instead of the npm package.

This adds a socket.io-client/browser subpath export pointing to that bundle, with the existing ESM type declarations:

import { io } from "socket.io-client/browser";

Changes

• packages/socket.io-client/package.json: add a ./browser entry to exports, mapping types to ./build/esm/index.d.ts and default to ./dist/socket.io.esm.min.js (both paths are already included in the published files).
• packages/socket.io-client/test/browser-export.ts: new tests asserting that the ./browser export is declared, that the files it points to exist, and that the subpath resolves through the package name.
• packages/socket.io-client/test/index.ts: register the new test file.

Tests

• npm run compile -ws --if-present — all workspaces compile successfully.
• mocha --import=tsx --exit test/browser-export.ts test/url.ts (in packages/socket.io-client) — 12 passing (3 new browser export tests, 9 existing url tests).
• npm run format:check (in packages/socket.io-client) — all matched files use Prettier code style.
• Additionally verified by hand that require.resolve("socket.io-client/browser") resolves to dist/socket.io.esm.min.js and that the bundle exports io, Manager, Socket and protocol (5).

Fixes #5383

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