Add One-Click Unsubscribe and Filtered Subscriptions View

Community & Support: [LinkedIn Group](https://www.linkedin.com/groups/14656108/) · [Slack #project-nest](https://owasp.slack.com/archives/project-nest)

Active project leaders: Arkadii Yakovets -- [GitHub](https://github.com/arkid15r/) · [LinkedIn](https://www.linkedin.com/in/arkid15r/) · [Slack](https://owasp.slack.com/team/U060W3NKLTF); Kate Golovanova -- [GitHub](https://github.com/kasya/) · [LinkedIn](https://www.linkedin.com/in/kate-golovanova/) · [Slack](https://owasp.slack.com/team/U07PWB1JZ6Z)

[Contributing](https://github.com/owasp/nest/blob/main/CONTRIBUTING.md) · [Code of Conduct](https://github.com/owasp/nest/blob/main/CODE_OF_CONDUCT.md) · [GSoC Mentors](https://github.com/owasp/nest/blob/main/MENTORS.md)

## Description

Users need the ability to easily unsubscribe from emails and view a personalized snapshot directly from the links in their digest emails. This sub-issue adds the one-click unsubscribe backend logic and the token-based link logic so users can view their filtered snapshot data securely without needing to log in.

## Changes
- Added a one-click Unsubscribe backend endpoint to handle the unsubscribe link from emails.
- Added a backend GraphQL query to fetch a user's subscription securely using their email token.
- Updated the Snapshot frontend page to read the token from the URL.
- Added a "Your Subscribed Entities" section on the frontend to display their personalized Pull Requests, Issues, and Releases.

**Are you going to work on implementing this?**

- [x] Yes
- [ ] No