perf(Preview): parallelize store loading and skip monitoring

- Load GlanceStore and InsightsStore concurrently using async let
- Add startMonitoring parameter to InsightsStore.initializeIfNeeded()
- Skip directory monitoring in previews to reduce initialization time

Author: webcpu

Packages/ClaudeUsage/Sources/App/AppEnvironment+Preview.swift

@@ -18,12 +18,11 @@ public struct PreviewEnvironment: PreviewModifier {
     public static func makeSharedContext() async throws -> AppEnvironment {
         print("\(timestamp()) PreviewEnvironment: Making shared context")
         let env = AppEnvironment.live()
-        print("\(timestamp()) PreviewEnvironment: glanceStore.loadData start")
-        await env.glanceStore.loadData()
-        print("\(timestamp()) PreviewEnvironment: glanceStore.loadData end")
-        print("\(timestamp()) PreviewEnvironment: insightsStore.loadData start")
-        await env.insightsStore.loadData()
-        print("\(timestamp()) PreviewEnvironment: insightsStore.loadData end")
+        print("\(timestamp()) PreviewEnvironment: loading stores in parallel")
+        async let glance: () = env.glanceStore.loadData()
+        async let insights: () = env.insightsStore.initializeIfNeeded(startMonitoring: false)
+        _ = await (glance, insights)
+        print("\(timestamp()) PreviewEnvironment: stores loaded")
         return env
     }
 

Packages/ClaudeUsage/Sources/Insights/Stores/InsightsStore.swift

@@ -41,12 +41,14 @@ public final class InsightsStore {
 
     // MARK: - Public API
 
-    func initializeIfNeeded() async {
+    func initializeIfNeeded(startMonitoring: Bool = true) async {
         guard !hasInitialized else { return }
         hasInitialized = true
 
-        await service.startMonitoring { [weak self] in
-            Task { await self?.loadData() }
+        if startMonitoring {
+            await service.startMonitoring { [weak self] in
+                Task { await self?.loadData() }
+            }
         }
         await loadData()
     }