fix: guard expo-notifications against Expo Go crash on import

SDK 53+ removed push notification support from Expo Go, causing the
module to throw at require-time. The static import in notifications.ts
propagated the error to _layout.tsx and both tab screens, making expo-
router report missing default exports and crash the app.

Switch to a try/catch require() so the module initialises safely in
Expo Go (Notifications stays null, all functions become no-ops) while
still working correctly in EAS / development builds.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/notifications.ts

@@ -1,4 +1,4 @@
-import * as Notifications from "expo-notifications";
+import type * as NotificationsType from "expo-notifications";
 import {
   loadNotifSettings,
   loadNotifThresholdLastFired,
@@ -7,6 +7,11 @@ import {
 import type { ClaudeUsageResponse } from "@/types/claude";
 import type { CodexUsageResponse } from "@/types/codex";
 
+// expo-notifications push notifications were removed from Expo Go in SDK 53.
+// Use require() so the initialization error is caught gracefully in Expo Go.
+let Notifications: typeof NotificationsType | null = null;
+try {
+  Notifications = require("expo-notifications") as typeof NotificationsType;
   Notifications.setNotificationHandler({
     handleNotification: async () => ({
       shouldShowAlert: true,
@@ -16,13 +21,18 @@ Notifications.setNotificationHandler({
       shouldSetBadge: false,
     }),
   });
+} catch {
+  // Running in Expo Go or native module unavailable — notifications disabled.
+}
 
 export async function requestPermissions(): Promise<boolean> {
+  if (!Notifications) return false;
   const { status } = await Notifications.requestPermissionsAsync();
   return status === "granted";
 }
 
 export async function getPermissionStatus(): Promise<string> {
+  if (!Notifications) return "undetermined";
   const { status } = await Notifications.getPermissionsAsync();
   return status;
 }
@@ -35,6 +45,7 @@ export async function scheduleDailyDigest(
   claudeUsage: ClaudeUsageResponse | null,
   codexUsage: CodexUsageResponse | null
 ): Promise<void> {
+  if (!Notifications) return;
   try {
     await Notifications.cancelScheduledNotificationAsync(DAILY_ID);
   } catch {}
@@ -68,6 +79,7 @@ export async function scheduleDailyDigest(
 }
 
 export async function cancelDailyDigest(): Promise<void> {
+  if (!Notifications) return;
   try {
     await Notifications.cancelScheduledNotificationAsync(DAILY_ID);
   } catch {}
@@ -128,7 +140,7 @@ export async function onUsageDataLoaded(
         claudeUsage,
         codexUsage
       );
-      if (alerts.length > 0) {
+      if (alerts.length > 0 && Notifications) {
         await Notifications.scheduleNotificationAsync({
           content: {
             title: "Low quota warning",