BD-1: Add performance benchmarking script

[szachovy]

Problem

There is no benchmarking or load testing capability. Performance changes (buffer pool, Gunicorn workers, caching) cannot be validated without measurable baselines. Apache Bench is single-threaded and doesn't model realistic Superset usage (async SQL queries, WebSocket polling, dashboard rendering).

Fix

Create scripts/benchmark.sh using wrk or curl loops that models a realistic Superset session: login throughput, dashboard API latency, Redis latency. The script should accept the VIP address as an argument.

This is a manual diagnostic tool — do NOT add it to CI.

Acceptance Criteria

• scripts/benchmark.sh created modeling realistic Superset session (login, dashboard API, Redis latency)
• Script accepts VIP address as argument (reads from project config or passed explicitly)
• Script documented as manual tool (not added to CI)