Update post layout

[maiertech]

Specification:

• Make the layout more consistent and appealing.
• Add recommended content on the right-hand side.
• Add newsletter sign-up at the bottom.

Inspiration:

• https://tailwindui.com/components/marketing/sections/content-sections#component-1f277327bc3a818c9212ddb202cc5e0f

[maiertech]

Done in #1253.