docs(proxy): add a Redis setup guide

[devin-ai-integration]

Summary

There was no page telling an operator how to actually stand Redis up and wire the proxy to it. The Redis story was spread across prod.md (two config snippets) and caching.md (cluster, sentinel, TLS, TTL, all framed as response caching), so the "how do I set this up for multiple pods" question had no home. This adds docs/proxy/redis_setup.md under Setup & Deployment, right after Production Best Practices.

It covers provisioning (managed options, the Bitnami helm chart, docker run redis:7 for local checks, sizing and allkeys-lru), then the config, making explicit that REDIS_* env vars alone do nothing until the config points at Redis, and why you want both router_settings and the cache block: the former backs cooldowns and usage/latency routing, the latter backs the coordination Redis behind rate limits, budgets, cache invalidation, the pod lock and scheduled jobs. general_settings.coordination_redis is documented for the case where you want coordination without a response cache, or on a separate Redis. It closes with verification (show_no_redis_warning from /health/readiness/details, the Admin UI banner disappearing, redis-cli --scan) and the operational follow-ups (transaction buffer, simple-shuffle, the litellm_redis_* metrics, max_connections).

Deeper topologies stay in caching.md and this links there rather than duplicating them.

Companion to #857, which lists what breaks without Redis and will link here; the banner added in BerriAI/litellm#36495 points at that page.

Link to Devin session: https://app.devin.ai/sessions/c91185109405404bbb87c4967a1346b0
Requested by: @mateo-berri

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview	Aug 13, 2026 3:09am

[mateo-berri]

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