Fix browser export interop by routing bundlers to CJS-typed UMD artifact

[Copilot]

Since less is "type": "module", bundlers resolving the "browser" export to dist/less.js can interpret the UMD file as ESM and lose default-import interop. This updates the browser export target to a CJS-typed path while preserving existing UMD artifacts.

• Export map alignment for browser bundlers

  • exports["."].browser now points to ./dist/less.cjs instead of ./dist/less.js.
  • Added explicit subpath export for ./dist/less.cjs.

• Build output update (no format rewrite)

  • Rollup browser build now emits an additional dist/less.cjs file with the same UMD output shape as dist/less.js.
  • dist/less.js and dist/less.min.js remain unchanged as published artifacts.

• Contract test update

  • Updated export-pattern checks to assert the browser entry is ./dist/less.cjs and that the file exists.

{
  "exports": {
    ".": {
      "browser": "./dist/less.cjs",
      "import": "./lib/less-node/index.js",
      "require": "./dist/less-node.cjs"
    }
  }
}