perf: reduce startup request fanout

Avoid repeated sidebar session and worktree refreshes
Limit concurrent GitHub PR status checks
Reuse cached worktree root resolution

packages/ui/src/stores/useGlobalSessionsStore.ts

@@ -23,7 +23,7 @@ type GlobalSessionsState = {
   archiveSessions: (ids: Iterable<string>, archivedAt?: number) => void;
 };
 
-const PAGE_SIZE = 200;
+const PAGE_SIZE = 500;
 
 let inflightLoad: Promise<LoadResult> | null = null;