fix(packaging): add exports map so default import works under Vite/Vitest

[MatthewHarrigan]

Fixes #1654.

Changes

Adds an exports field to package.json so each module environment resolves auth0-js to the correct bundle. No code changes; no dist/ rebuild; no build/test infrastructure changes.

"exports": {
  ".": {
    "import":  "./dist/auth0.min.esm.js",
    "require": "./dist/auth0.min.js",
    "default": "./dist/auth0.min.esm.js"
  },
  "./dist/*":        "./dist/*",
  "./build/*":       "./build/*",
  "./package.json":  "./package.json"
}

Why this works:

• import condition → ESM bundle. Fixes the bug reported in v10.0.0: "type": "module" + UMD main breaks default import under Vite/Vitest (import auth0 from 'auth0-js' yields undefined) #1654: Vite/Vitest (and any modern bundler that respects "type": "module") were resolving the package to the UMD main, loading it as ESM, finding no top-level export statements, and handing consumers undefined for the default import. Routing import directly at the ESM bundle restores the documented import auth0 from 'auth0-js' usage.
• require condition → UMD bundle. Jest-style transformers that read exports will pick up the UMD file and execute it as CJS, where exports.X = ... writes work correctly.
• default fallback → ESM bundle for any environment that doesn't match the above conditions.
• ./dist/* and ./build/* wildcards preserve deep-path imports (auth0-js/dist/auth0.min.esm.js etc.) that some consumers have adopted as a workaround for v10.0.0: "type": "module" + UMD main breaks default import under Vite/Vitest (import auth0 from 'auth0-js' yields undefined) #1654. Once this lands the workaround is unnecessary, but keeping the wildcards avoids breaking anyone who's still on the workaround.
• ./package.json is exposed because some tools (TypeScript, bundlers) read it.

Honest scope

This PR fixes the ESM consumer path (the bug in #1654 — the one breaking the documented import). The pure-Node CJS require() path remains broken on v10 because "type": "module" causes Node to load .js files as ESM regardless of the require condition target, so the UMD bundle's exports.X = ... writes still have no effect. Fixing that properly requires renaming the UMD output to .cjs (or splitting the build), which is out of scope here. Filing as a separate concern if maintainers want.

Verified on a baseline of v10.0.0 master (pre-PR): require('auth0-js') already returns [Module: null prototype] {} — so this PR neither fixes nor regresses CJS.

References

• Bug report with full reproduction: v10.0.0: "type": "module" + UMD main breaks default import under Vite/Vitest (import auth0 from 'auth0-js' yields undefined) #1654
• README documents import auth0 from 'auth0-js' then new auth0.WebAuth({...}) — the exact pattern broken by v10 packaging.

Testing

All existing local CI gates green against this branch:

Gate	Result
npm run lint	clean
npm run build	produces all 4 expected artifacts
npm test	658 passing
npm run test:es-check:es5	pass
npm run test:es-check:es2015:module	pass

I didn't run npm run smoke:modern or the BrowserStack e2e tests — those need toolchain I don't have set up locally. Happy to add coverage if the reviewer suggests a specific gate.

Resolution probe (Node 22, ESM consumer)

Against the unmodified v10.0.0:

default import: undefined
namespace keys: []

Against this branch:

default import: { Authentication: [Function], Management: [Function], WebAuth: [Function], version: '10.0.0' }
default.Authentication: function
default.WebAuth: function

• This change adds unit test coverage — N/A, packaging-only metadata change
• This change adds integration test coverage — N/A, packaging-only metadata change

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All tests and linters described in the Develop section run without errors