Stream job results via SSE

Server-Sent Events stream for real-time job results. Events sent: - **status**: Initial job status and progress updates - **result**: Each extracted result as it completes - **complete**: Final status when job finishes - **error**: Error notifications The stream sends heartbeat comments every 15 seconds to keep connections alive through proxies. Example usage with curl: ```bash curl -H "Authorization: Bearer rf_your_key" \ -H "Accept: text/event-stream" \ https://api.refyne.dev/api/v1/jobs/{id}/stream ```

curl -H "Authorization: Bearer rf_your_key" \
     -H "Accept: text/event-stream" \
     https://api.refyne.dev/api/v1/jobs/{id}/stream

curl -X GET "http://localhost:8080/api/v1/jobs/string/stream"

[
  {
    "data": {
      "job_id": "string",
      "page_count": 0,
      "status": "string",
      "urls_queued": 0
    },
    "event": "status",
    "id": 0,
    "retry": 0
  }
]

{
  "detail": "Property foo is required but is missing.",
  "errors": [
    {
      "location": "string",
      "message": "string",
      "value": null
    }
  ],
  "instance": "https://example.com/error-log/abc123",
  "status": 400,
  "title": "Bad Request",
  "type": "https://example.com/errors/example"
}