feat(site): evaluate real Web Push notifications

[DevSecNinja]

Problem

Wazzup currently uses browser Notification permission plus service-worker sync/periodic-sync hooks. That is useful for best-effort app-open or browser-managed checks, but it is not a guaranteed server-initiated notification path.

Goal

Evaluate and design true Web Push support so a new briefing generated by GitHub Actions can notify subscribed devices without requiring the app to be open.

Scope

• Investigate Push API support across desktop Edge/Chrome, Android Chrome/Edge, and iOS/iPadOS installed web apps.
• Decide where to store push subscriptions for a GitHub-native/static architecture.
• Decide how to manage VAPID keys/secrets.
• Design a GitHub Actions sender step or lightweight serverless endpoint that can send a notification after a successful briefing run.
• Preserve a graceful fallback for browsers that only support foreground/open-app notification checks.

Acceptance criteria

• A documented implementation plan with browser support matrix and security/privacy considerations.
• A chosen subscription storage/sender strategy that fits the project architecture.
• Follow-up implementation tasks if the plan is accepted.