Fix limit parameter to respect config.jobCount for TheirStack fetcher

[Copilot]

The limit parameter was always defaulted to 10 even when not provided as a query parameter, preventing fetchTheirStack from falling back to config.jobCount/JOB_COUNT.

Changes

• Changed limit default from 10 to undefined in /api/pipeline/step1 endpoint (line 92 of backend/src/routes/pipeline.ts)

This allows fetchTheirStack to use its existing fallback logic:

const to = options.range
  ? options.range.to
  : Math.min(deduped.length, options.limit ?? config.jobCount);

When no limit query param is provided, the function now correctly uses the configured JOB_COUNT environment variable instead of always using 10.

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