feat: Add Web Push notifications and multiple UX improvements

- Add PWA manifest and service worker for push notifications
- Implement VAPID key generation and push subscription management
- Add push notification API endpoints (/api/push/*)
- Add push_subscriptions table to database schema
- Update notification settings UI with push support and iOS hints
- Fix translation issue showing "{ task } created" - add missing keys
- Fix mobile sidebar visibility for iOS home screen app
- Change default task filter from "all" to "open" (excludes done tasks)
- Add "Open" filter option to show only todo + inProgress tasks

client/src/App.tsx

@@ -337,6 +337,14 @@ function AppContent() {
         <AppSidebar user={user} />
         <SidebarInset>
           <div className={`min-h-screen bg-background flex flex-col ${adhdEnabled ? 'adhd-mode' : ''} ${adhdEnabled && adhdSettings.reducedAnimations ? 'reduced-motion' : ''} ${adhdEnabled && adhdSettings.largerTargets ? 'larger-targets' : ''}`}>
+            {/* Mobile Header with Sidebar Toggle */}
+            <header className="sticky top-0 z-50 flex items-center gap-3 px-4 py-3 bg-background/80 backdrop-blur-xl border-b border-border/50 md:hidden">
+              <SidebarTrigger className="h-9 w-9" />
+              <div className="flex items-center gap-2">
+                <img src="/favicon.png" alt="Logo" className="w-7 h-7 rounded-lg" />
+                <span className="font-bold text-lg">{t('app.title')}</span>
+              </div>
+            </header>
             <main className="flex-1 p-4 md:p-6 max-w-screen-2xl mx-auto w-full relative">
               <Switch>
                 <Route path="/">