Add comprehensive integration tests for Miroir with 3 Meilisearch nodes
via docker-compose. Tests cover:
- Document round-trip with distribution verification (1000 docs)
- Search covers all shards (100 docs with unique keywords)
- Facet aggregation across shards (100 docs, 3 colors)
- Offset/limit paging consistency (50 docs, 5×paged vs single)
- Settings broadcast to all nodes (synonyms test)
- Task polling for large batches (500 docs)
- Node failure with RF=2 (requires docker-compose-dev-rf2)
Also added integration test README with setup and running instructions.
Per plan §8: Integration tests validate end-to-end behavior including
document distribution, shard coverage, facet aggregation, paging, settings
broadcast, task polling, and node failure with RF=2.
Closes: miroir-89x (Phase 9 — Testing)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
