ntfy_push_core: initial module commit

[nurefexc]

PR Description for OCA/social

Module Name: ntfy_push_core

Summary

This PR introduces a new module to provide asynchronous push notifications for Odoo using the ntfy.sh protocol. It allows users to receive real-time Odoo notifications (messages, mentions, activities) directly on their mobile devices or desktops via the ntfy app or server.

Key Features

• Asynchronous Queueing: Notifications are not sent directly during the write/create process. Instead, they are queued and processed via a dedicated Cron job to ensure Odoo's UI performance remains unaffected by network latency.
• Secure Topic Generation: Each user gets a unique, secure topic URL generated using a SHA-224 hash based on the database UUID and user ID, preventing unauthorized access to notification streams.
• Flexible Configuration: Supports both the official https://ntfy.sh server and self-hosted instances.
• User-Friendly Setup: Users can easily switch their notification preference to "ntfy.sh" and instantly get their subscription URL with a QR-like link.
• Deep Linking: Notifications include a click-through URL that takes the user directly to the relevant Odoo record.

Technical Notes

• Inherits from mail.thread to hook into the message posting process.
• Includes automated tests covering URL generation, user settings, and server consistency checks.
• Fully compliant with OCA linting and formatting standards (Black, Ruff, Pylint).

Testing Instructions

1. Install the module.
2. Go to Settings > Technical > System Parameters and set ntfy.server_url (optional, defaults to ntfy.sh).
3. Go to your User Profile > Preferences and set "Notification" to ntfy.sh.
4. Copy the generated URL into your ntfy mobile app.
5. Post a message on any document where you are a follower; you should receive a push notification via the cron job.