Remove Typefully from sponsors section

Author: kjaymiller

.gitignore

@@ -230,3 +230,5 @@ marimo/_lsp/
 __marimo__/
 .venv
 output
+.issues/
+AGENTS.md

_layouts/_includes/join_us.html

@@ -29,9 +29,6 @@ <h2>Support Black Python Devs</h2>
   <section>
     <h3>Corporate Sponsors</h3>
     <div class="grid">
-      <article class="sponsor">
-        <img src="/assets/images/typefully_brand.png" alt="Typefully Logo" />
-      </article>
       <article class="sponsor">
         <img src="/assets/images/gnome-foundation-blue.png" alt="GNOME Foundation Logo" style="height: 2rem" />
       </article>