Add session timeout for connected wallet state

[collinsadi]

Long-lived wallet sessions on shared devices increase exposure.

Add configurable idle timeout that locks sensitive views and clears ephemeral session keys.

Acceptance criteria:

• Timeout configurable in settings.
• Sensitive views require reconnect.
• Does not delete persisted encrypted backup.

[udoyechinenyevictoria]

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

Hello! Please can I work on this issue?

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