Swap deadline & explicit slippage parameters

[DevMuhdishaq]

Description
swap/pool_swap should accept a user-supplied min_amount_out and a deadline ledger timestamp to protect against slippage and stale execution, standard for AMM safety.

Direction

• Add min_amount_out: i128 and deadline: u64 parameters (or an overloaded swap_with_protection).
• Reject if env.ledger().timestamp() > deadline (Expired error) or output < min_amount_out (SlippageExceeded error).
• Keep the existing max_slippage_bps global as a fallback ceiling.

Acceptance criteria

• Swap succeeds when output ≥ min_amount_out and before deadline.
• Swap reverts with SlippageExceeded when output would be below min_amount_out (no state change).
• Swap reverts with Expired past the deadline.
• Existing swap tests updated/added; all pass.

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[GBOYEE]

Hey, I'd like to help with this. I can handle this one. I'll build the UI per the acceptance criteria. Will send a PR for this after assignment.

[ahmadogo]

Hello Maintainer!!
I am a software engineer and an open source contributor. I would like to work on this issue please

[grantfox-oss]

🦊 GrantFox — @ahmadogo has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #215)
2. Your PR will be reviewed by the StelTade maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@ahmadogo's PR #236 was approved and merged by @DevMuhdishaq.

🏆 @ahmadogo: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (697 total points). Track your full progress on GrantFox.

👏 Great work, @ahmadogo! Keep contributing to StelTade.