For repos with 1000+ issues where less than 20% are dirty,
incremental export reads the existing JSONL, merges only
changed issues, and writes back - avoiding full re-export.
- Add exportToJSONLIncrementalDeferred as new default export path
- Add shouldUseIncrementalExport to check thresholds
- Add performIncrementalExport for merge-based export
- Add readJSONLToMap helper for fast JSONL parsing
- Falls back to full export when incremental is not beneficial
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
