fix(app-server): advance zero-limit thread pages

Clamp a requested zero page size to one while preserving existing cursor compatibility. An isolated Mac stdio observation exercised zero, legacy and invalid cursors against three fixture threads.

crates/app-server/src/stdio.rs

@@ -1064,7 +1064,7 @@ pub(crate) async fn dispatch_stdio_request_with_writer<W: AsyncWrite + Unpin>(
                     .partition_point(|thread| thread.id.as_str() <= cursor)
             });
             let remaining = &loaded.threads[start..];
-            let count = limit.unwrap_or(remaining.len()).min(remaining.len());
+            let count = limit.unwrap_or(remaining.len()).max(1).min(remaining.len());
             let data = remaining[..count]
                 .iter()
                 .map(|thread| thread.id.clone())