Introduce initial push notification support by adding a new `notification.py` module for VAPID key pair generation (EC P-256), a `PushView` endpoint serving the public key, and a `push.js` client that fetches the key and subscribes the service worker with `userVisibleOnly` flag. The service worker push listener is refactored to check notification permission and handle click events. The `app.html` template now includes the push script as a module, and the application startup calls `get_notifications()` to ensure keys exist. Note: FCM-based push on Chrome/Opera remains non-functional due to unresolved compatibility issues.
BordedDev
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