[Sync to prerelease] Blog post: The Quarto Blog has a new home (#2020)

* Blog post: Quarto Blog has a new home

* Add callout to blog listing page announcing move

* Fix YAML in new blog post and hide retired signup form via CSS

* Update blog post date to 2026-05-07

* Sync thumbnail.svg with PNG (add BLOG labels)

* Rename post directory to 2026-05-07 to match date

* Remove Mailchimp email subscription form

The Quarto blog is moving to the Posit Open Source site, where readers
can subscribe to the Glimpse Open Source newsletter for email updates.
Retire the legacy quarto.org Mailchimp form rather than just hiding it
behind CSS, since it has no future maintainer once the blog moves.

(cherry picked from commit 10476ba)

Co-authored-by: Christophe Dervieux <christophe.dervieux@gmail.com>

Author: github-actions[bot]

docs/blog/index.qmd

@@ -9,8 +9,13 @@ listing:
   categories: true
   feed: true
 page-layout: full
-margin-header: signup.html
 title-block-banner: true
 search: false
 image: quarto-blog-v2.png
 ---
+
+::: {.callout-note appearance="simple" icon=false}
+## The Quarto Blog has a new home
+
+The Quarto blog has moved to the [Posit Open Source blog](https://opensource.posit.co/blog/?q=source%3Aquarto). All past and future Quarto posts now live there alongside posts from our other open-source projects. See the [announcement post](posts/2026-05-07-new-blog-home/) for details.
+:::

docs/blog/posts/2026-05-07-new-blog-home/index.qmd

@@ -0,0 +1,22 @@
+---
+title: "The Quarto Blog has a new home!"
+description: |
+  The Quarto blog has moved to the Posit Open Source website.
+  Subscribe to the Glimpse Open Source newsletter or update your RSS reader to keep getting Quarto news.
+author: The Quarto Team
+date: "2026-05-07"
+categories:
+  - Announcement
+image: thumbnail.png
+image-alt: "The Quarto logo with an arrow pointing to the Posit Open Source logo, illustrating that the Quarto blog has moved to the Posit Open Source website."
+---
+
+We're happy to announce that the Quarto blog has officially moved to its new home on the [Posit Open Source website](https://opensource.posit.co/blog/?q=source%3Aquarto). All previous Quarto posts have already been migrated, alongside posts from other Posit Open Source projects — so you'll find Quarto news in good company with [Shiny](https://opensource.posit.co/blog/?q=source%3Ashiny), [Tidyverse](https://opensource.posit.co/blog/?q=source%3Atidyverse), and the rest of the Posit Open Source ecosystem.
+
+The rest of `quarto.org` — including the [Guide](/docs/guide/), [Reference](/docs/reference/), [Gallery](/docs/gallery/), and download pages — is staying put. Only the blog is moving.
+
+We are retiring the email subscription list attached to this site. To keep getting Quarto news by email, sign up for **Product Updates - Open Source** (the Glimpse Open Source newsletter) on the [Posit subscription management page](https://posit.co/about/subscription-management).
+
+If you follow the blog through RSS, please update your reader. The current feed at `https://quarto.org/docs/blog/index.xml` will not receive new Quarto posts after this announcement. The new "all posts" feed lives at <https://opensource.posit.co/blog/index.xml>, and you can also pick more focused feeds — by topic, language, or event — from the [Posit Open Source subscribe page](https://opensource.posit.co/subscribe/).
+
+Thanks for reading, and see you on the [new blog](https://opensource.posit.co/blog/?q=source%3Aquarto)!