chore: remove blog, open-source and news sections

- Delete the blogs, opensource-projects and notifications trees
- Drop their nav entries and i18n keys
- Point the nav at the new open-source site instead
- Drop the opensource-projects sitemap priority

rspress.config.ts

@@ -107,7 +107,6 @@ type SitemapOverrides = Record<string, Omit<CustomMapsOption[string], "loc">>
 const PRIORITISED_ROUTES = [
   ["/products/", "1.0"],
   ["/services/", "1.0"],
-  ["/opensource-projects/", "0.8"],
 ] as const
 
 /**