docs: sync diagnostics pages and the Vite plugin's test environment - #1665

Changed pages include:

• index.html - view
• glossary.html - view
• reference.html - view
• building-apps/app-structure.html - view
• building-apps/deployment.html - view
• building-apps/environment.html - view
• building-apps/head-and-metadata.html - view
• building-apps/middleware-and-api-routes.html - view
• building-apps/server-functions.html - view
• building-apps/sessions-and-auth.html - view

There are more changes not included in the list