Simplify connection config and client IP resolution

[dgarcia360]

Motivation

Per-request settings were resolved from several overlapping places, and client IP extraction reimplemented proxy-header parsing by hand.

Solution

• base_url is resolved once from connection-level configuration (query params / session), with https://app.biel.ai as the default, instead of being merged through per-call tool arguments.
• The client IP now comes from the socket peer; forwarded headers are handled by uvicorn's built-in proxy-headers support, configured through the standard FORWARDED_ALLOW_IPS env var (exposed in docker-compose.yml).

How to test

1. docker compose up (or python biel_mcp_server.py).
2. Connect an MCP client, e.g. npx mcp-remote "http://localhost:7832/sse?project_slug=YOUR_SLUG", and ask a question — responses are unchanged.
3. Self-hosted instances keep working by passing base_url as a connection query param.