Deprecate duplicated code in WebSocket and HTTP servers

Based on feedback from PR #49, the duplicated code in `server/app.py` and `server-https/app.py` will be deprecated in the future. The current code duplication is intentional to ensure appropriate deployment and ease of switching between socket and HTTP servers.

This issue is to track the future cleanup and deprecation of the current architecture once a unified or improved approach is adopted.

**Context:**
- The extraction of the shared RAG module (in PR #49) was reverted to maintain the duplication for now.
- Moving forward, this duplicated architecture should be revisited for deprecation.

Start by comparing server/app.py and server-https/app.py, then review PR #49 and its reverted shared RAG module extraction. The issue does not define the replacement architecture; completion requires an agreed unified approach followed by deprecating the duplicated server code.

Written by the indexing model from the issue text.