fix(mcp): correct import path for search_docs endpoint (#27)

* feat(rag): step 6B retrieval tool (MCP) with tests

- Add mcp-server/tools/search_docs.py with real embedding query
- Update mcp-server/server.py to use new search tool
- Add tests/rag/test_retrieval_topk.py with top-k retrieval tests
- Query → embed → cosine → top-k (k=3–5) functionality
- Return passages + metadata (doc_id, chunk_id, score)
- Fallback to mock results when RAG components unavailable

Awaits CI for merge.

* fix(mcp): correct import path for search_docs endpoint

- Rename mcp-server/ to mcp_server/ for proper Python package structure
- Add __init__.py to make it a proper package
- Update all references from mcp-server to mcp_server
- Fixes import error: mcp_server.tools.search_docs import search_documents_endpoint

* fix(docs): add version header to v0.6.2.md

Move Version: v0.6.2 to first line to satisfy docs-check CI

Author: haz3141