Implement Export and Import Dashboard Layouts

[Nanle-code]

Allow users to export their customized dashboard layout (widget positions and types) as JSON and import them to restore or share configurations.

Acceptance Criteria:

• Export layout button in settings
• Import layout from file or JSON paste
• Layout versioning for future compatibility
• Share layout via URL (encoded in hash)
• Restore previous layouts from history
• Validation prevents invalid imports

[Favourof]

@Favourof has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work on this issue.

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

[drips-wave]

Congratulations, @Favourof! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Favourof: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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