feat(update): add 15-minute auto-check interval for app updates (#66)

Reuses same checkForUpdates flow as manual button - all guards and UI
state transitions apply automatically.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: robinebers

src/hooks/use-app-update.ts

@@ -103,8 +103,15 @@ export function useAppUpdate(): UseAppUpdateReturn {
   useEffect(() => {
     mountedRef.current = true
     void checkForUpdates()
+
+    // Check every 15 minutes
+    const intervalId = setInterval(() => {
+      void checkForUpdates()
+    }, 15 * 60 * 1000)
+
     return () => {
       mountedRef.current = false
+      clearInterval(intervalId)
       if (upToDateTimeoutRef.current !== null) {
         clearTimeout(upToDateTimeoutRef.current)
       }