Add Valkey for AI documentation page with integration links and examples #434

Context

We'd like to contribute a documentation page that helps AI/ML developers discover how Valkey fits into their stack. Several integrations are now shipped and usable, but there's no central page on valkey.io pointing developers to them.

Problem

Developers building AI applications (RAG, agents, semantic caching, memory) have no single page on valkey.io showing what's available and how to get started. The information is scattered across module READMEs, third-party repos, and blog posts.

Proposal

Add a documentation page (topic or standalone) covering Valkey's AI ecosystem with links to completed integrations and getting-started examples.

Shipped integrations to feature:

Page structure:

• Brief intro: why Valkey for AI (low latency, vector search, persistence)
• Use cases: vector search/RAG, agent memory, semantic caching, session state
• Integration table with links and short descriptions
• Getting started: minimal code example for vector search with valkey-search
• Links to relevant blog posts and try-valkey cookbooks

Implementation

• One new markdown file in the topics directory
• Links to external repos and docs (no code changes needed)
• Easy to update as new integrations ship

Why this matters

• AI is Valkey's fastest growing use case
• Developers searching "valkey ai" or "valkey vector" should land on a useful page
• Centralizes information that's currently scattered across 4+ repos