Execute query with NDJSON streaming

Returns an NDJSON stream for large result sets, exports, and piping.

This is different from job SSE (GET /query/jobs/{id}/stream):

• /query/stream — NDJSON export of results. One event per line. For curl | jq, data pipelines.

• /query/jobs/{id}/stream — SSE progress tracking. For Web UI real-time updates.

• Response: Transfer-Encoding: chunked, one JSON object per line.

• Last line is always {"__meta": {...}} — stream summary.

• Supported request fields: q/query, from/earliest, to/latest, and variables.

• limit, offset, wait, profile, and format are rejected with 400.

• Client disconnect = cancellation.