Add page SEO integration guide

[hieuht09]

Summary

This PR adds a new comprehensive guide for Page SEO integration in Weaverse Hydrogen, helping developers wire Studio-configured SEO metadata into their storefront routes.

Key Sections Added

• Overview: Explains the flow of Weaverse SEO metadata and how the storefront retrieves and renders it.
• Catch-all route recipe: Guide on wiring Weaverse SEO for dynamic custom pages.
• Home / index route recipe: Outlines how Weaverse SEO integrates with the homepage, including fallback logic to code-defined default SEO.
• Template routes guide: Explains how to handle Shopify resource templates (products, collections, blogs, etc.) and let Shopify SEO take precedence.
• Register navigation: Added features/page-seo to docs.json so the new guide appears in the sidebar menu.