Refactor Zustand stores to use slices pattern for modularity

[Smartdevs17]

Description

Stores have grown large and mix concerns. Refactor to use Zustand slices pattern for better separation of concerns and testability.

Acceptance Criteria

• Store split by domain (subscription, wallet, notification, etc.)
• Slices with clear interfaces
• Cross-slice communication via events or selectors
• Store test coverage >80%
• Performance benchmark (selector optimization)
• Migration guide for existing store consumers

Technical Scope

• src/store/
• Edge: circular slice dependencies, selector recomputation, store hydration ordering

[senmalong]

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

i'd love to work on this

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

[danieloche635-bit]

@danieloche635-bit has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

will love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @danieloche635-bit to this issue.

[drips-wave]

Congratulations, @danieloche635-bit! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @danieloche635-bit: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊