fix(desktop): check relay accepted flag on engram publish

publish_agent_event now parses the response body as SubmitEventResponse
and verifies accepted == true. The relay can return HTTP 200 with
accepted: false on duplicate events or policy rejections — previously
this was treated as success. Matches the pattern in submit_event
(relay.rs:394).

Co-authored-by: Will Pfleger <pfleger.will@gmail.com>
Signed-off-by: Will Pfleger <pfleger.will@gmail.com>

desktop/src-tauri/src/managed_agents/fleet_update.rs

@@ -246,6 +246,16 @@ async fn publish_agent_event(
     if !response.status().is_success() {
         return Err(relay::relay_error_message(response).await);
     }
+
+    let result: relay::SubmitEventResponse = response
+        .json()
+        .await
+        .map_err(|e| format!("failed to parse publish response: {e}"))?;
+
+    if !result.accepted {
+        return Err(format!("relay rejected engram: {}", result.message));
+    }
+
     Ok(())
 }