Use Graffito's new icon from its repo

Claude-Session: https://claude.ai/code/session_01BZwA81Gq6wvExjGipi7ad5

Author: ObjSal

assets/icons/graffito.svg

@@ -678,7 +678,7 @@ <h3><img class="app-icon" src="assets/icons/chain-notes.svg" alt="" width="24" h
         </div>
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       <a class="card" href="https://github.com/ObjSal/graffito" target="_blank" rel="noopener">
-        <h3><img class="app-icon" src="assets/icons/chain-notes.svg" alt="" width="24" height="24"> Graffito</h3>
+        <h3><img class="app-icon" src="assets/icons/graffito.svg" alt="" width="24" height="24"> Graffito</h3>
         <p>Native Mac, iOS, and Android companion for notes on the Bitcoin blockchain: encrypted directed notes, coin control, RBF, sweep/consolidate, and watch-only identities signed by an external hardware wallet.</p>
         <div class="card-meta">
           <span class="tag bitcoin">Bitcoin</span>