feat: add push notification infrastructure with VAPID key generation and PWA manifest support

- Introduce push notification module with VAPID certificate generation, Web Push encryption, and subscription management
- Add push registration table index and database schema for storing user subscriptions
- Integrate push notification dispatch into existing notification creation flow via async background tasks
- Include PWA manifest, service worker, and install prompt UI elements in base template
- Register new push router and ensure certificate initialization on application startup
- Add configuration variables for VAPID private/public key file paths and subscription contact email
- Update JavaScript application entry point with PushManager and PwaInstaller modules
- Extend top navigation bar with hidden install and push enable buttons for authenticated users

devplacepy/templates/base.html

@@ -24,6 +24,10 @@
 
     <link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>&#x1f4bb;</text></svg>">
     <link rel="apple-touch-icon" href="/static/apple-touch-icon.png">
+    <link rel="manifest" href="/manifest.json">
+    <meta name="apple-mobile-web-app-capable" content="yes">
+    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
+    <meta name="apple-mobile-web-app-title" content="DevPlace">
 
     <link rel="stylesheet" href="/static/css/variables.css">
     <link rel="stylesheet" href="/static/css/base.css">
@@ -58,6 +62,12 @@
             </div>
             <div class="topnav-right">
                 {% if user %}
+                <button type="button" class="topnav-icon" data-pwa-install hidden title="Install DevPlace app" aria-label="Install DevPlace app">
+                    <span class="nav-bell">&#x2B07;&#xFE0F;</span>
+                </button>
+                <button type="button" class="topnav-icon" data-push-enable hidden title="Enable push notifications" aria-label="Enable push notifications">
+                    <span class="nav-bell">&#x1F515;</span>
+                </button>
                 <a href="/notifications" class="topnav-icon">
                     <span class="nav-bell">&#x1F514;</span>
                     {% set unread_count = get_unread_count(user["uid"]) %}