Add notification preferences for scan completion

[collinsadi]

Users must keep tab open during long scans to know when funds are found.

Add optional browser notification on scan complete and new ghost detection.

Acceptance criteria:

• Permission requested on opt-in.
• Notifications exclude amounts if privacy mode on.
• Works after background tab throttle.

[akinboyewaSamson]

@akinboyewaSamson has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi! I’m a full-stack developer with a strong blockchain background. I’d love to handle this issue and can deliver a clean, reliable solution. Kindly assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @akinboyewaSamson to this issue.

[Macnelson9]

@Macnelson9 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi team, I'd like to take on this issue.

I specialize in Rust development, smart contract engineering, and frontend development with Next.js, React, and TypeScript. My experience allows me to bridge on-chain functionality with intuitive user experiences, ensuring both technical correctness and usability.

I'll follow the existing codebase conventions, communicate progress clearly, and deliver a high-quality solution within the expected timeline.

Thank you for your consideration.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Macnelson9 to this issue.