[Frontend] Add transaction simulation/preview before signing

[Xoulomon]

Suggested Tier: Medium (150 pts)

Description:
Reduce failed transactions by simulating contract calls via Soroban RPC and showing expected outcome/fees before the user signs.

Tasks:

• Call Soroban simulateTransaction before submission for contribute/join/payout
• Display estimated resource fees and expected state change
• Block submission and show a clear error if simulation fails
• Cache simulation results briefly to avoid redundant RPC calls

Acceptance Criteria:

• A call that would fail on-chain is caught at simulation and not submitted
• Estimated fee shown is within a reasonable margin of the actual fee charged

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[rejoicetukura-blip]

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

I’m interested in contributing to this Drips issues and helping improve the ecosystem through bug fixes, feature

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

[drips-wave]

Congratulations, @rejoicetukura-blip! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @rejoicetukura-blip: 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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