feat(ai-stack): wire /ai-stack route and add to sitemap

Registers /ai-stack route in App.jsx routing table. Adds sitemap
entry with changefreq=daily (data updates nightly) and priority=0.8
to signal freshness to crawlers — appropriate for a data product page
that changes every 24 hours.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Author: anshulbasia27