Remove duplicate paragraph at end of advanced vector store config

Clean up duplicated introduction paragraph that was repeated at the end
of the advanced vector store configuration documentation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: abrookins

docs/vector-store-advanced.md

@@ -800,5 +800,3 @@ class ZeroDowntimeMigrator:
         print("✅ Cutover completed successfully")
         return final_check
 ```
-
-This documentation covers advanced architectural patterns for vector store configuration, focusing on flexible factory patterns, custom implementations, and data migration strategies that work across different backends.