landing(agents): add an Example prompt card to the agent-friendly section

Show the one-liner an operator would actually hand an agent to drive a
Keysat integration (review the docs, gate paid features behind a Pro
license, connect BTCPay). Reuses the install-card + navy code-block styling;
sits below the three capability cards, above the integration-guide link.

index.html

@@ -318,6 +318,12 @@ pre.code .p { color:rgba(245,241,232,0.55); }
 /* ---------- Agent-friendly section ---------- */
 .agent-grid { display:grid; grid-template-columns:repeat(3, 1fr); gap:24px; }
 @media (max-width: 880px) { .agent-grid { grid-template-columns:1fr; } }
+.agent-prompt-card { margin-top:24px; }
+.agent-prompt {
+  background:var(--navy-950); color:var(--cream-50);
+  border-radius:10px; padding:18px 20px;
+  font-family:var(--font-mono); font-size:13.5px; line-height:1.7;
+}
 
 /* ---------- Tier comparison ---------- */
 .tier-grid { display:grid; grid-template-columns:repeat(3, 1fr); gap:20px; }
@@ -908,6 +914,11 @@ fmt.<span class="f">Printf</span>(<span class="s">"licensed for %s, expires %s\n
         <p>HMAC-signed event deliveries on every license / invoice / subscription state change. Every error response carries a stable machine-readable code (<code>tier_cap</code>, <code>not_found</code>, <code>license_revoked</code>) so agents branch deterministically.</p>
       </div>
     </div>
+    <div class="agent-prompt-card install-card">
+      <div class="cap">Example prompt</div>
+      <p>Hand the whole integration to an agent. Point it at the docs and describe what to gate:</p>
+      <div class="agent-prompt">&ldquo;Review the Keysat docs on GitHub and integrate Keysat licensing into my app. Require a Pro license for my paid features (CSV export, scheduled reports, and the public API), and connect it to my BTCPay Server.&rdquo;</div>
+    </div>
     <div style="margin-top:32px; text-align:center">
       <a class="btn ghost" href="https://docs.keysat.xyz/agent.html">Agent integration guide &rarr;</a>
     </div>