feat(ai): enhance RAG with Milvus integration, query rewrite, multi-path retrieval and refactor (#1458)

* refactor(ai): reorganize RAG components with multi-path retrieval and merge

- Reorganize RAG components into indexers, retrievers, loaders, mergers, rerankers, and query packages
- Add Milvus multi-path retrieval support (Dense, BM25 Sparse, Hybrid)
- Add RRF (Reciprocal Rank Fusion) merge layer with deduplication
- Add score normalization strategies (MinMax, ZScore, Rank, Softmax, Sigmoid, Log)
- Add comprehensive Milvus unit tests and E2E workflow tests
- Fix deduplication to handle documents without IDs using content hash
- Fix Milvus SDK dependency compatibility with Go 1.25+

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat(ai): enhance RAG with query rewrite, multi-path retrieval and merge

- Add query rewrite processor for enhanced query optimization
- Implement multi-path retrieval with merge capabilities
- Add comprehensive E2E tests for RAG workflows
- Enable query processor by default in config
- Add RAG test helpers and utilities

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: add AI_CHANGES_SUMMARY.md to gitignore

* chore: remove AI_CHANGES_SUMMARY.md

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: YuZhangLarry

.gitignore

@@ -47,3 +47,9 @@ vendor/
 
 # dubbo cp cache
 app/dubbo-cp/cache
+
+# environment files
+.env
+.env.local
+.env.*.local
+AI_CHANGES_SUMMARY.md