This PR adds native FormData and file upload support to the Feathers HTTP transport.

Changes

Client (packages/feathers/src/client/fetch.ts)

• Auto-detects FormData in request body and skips JSON serialization
• Lets the browser set the correct Content-Type header with multipart boundary

Server (packages/feathers/src/http/middleware.ts)

• Added multipart/form-data parsing in bodyParser() using native request.formData()
• Converts FormData to plain object (single values unwrapped, multiple values become arrays)

Test Fixture (packages/feathers/fixtures/index.ts)

• Replaced @whatwg-node/server with a native Node.js adapter
• Fixes a bug where duplicate FormData keys were being lost

Usage

// Client
const formData = new FormData()
formData.append('file', fileInput.files[0])
formData.append('description', 'My upload')

await app.service('uploads').create(formData)

// Server receives:
{
  file: File,
  description: 'My upload'
}

// Multiple values become arrays:
{
  files: [File, File, File]
}

Limitations

• REST only - FormData is not supported over Socket.io
• Buffered - Uses native request.formData() which buffers into memory. For large files, use presigned URLs to upload directly to cloud storage.

Breaking Changes

None. This is additive functionality.