Add a protocol fee deduction on settlement that sends a percentage of repayment proceeds to the treasury

[Chucks1093]

Summary

The settlement function currently distributes the full repayment to investors with no protocol cut. A configurable protocol fee deducted from the repayment amount before investor distribution would sustain the protocol treasury.

Scope

• Add set_settlement_fee(fee_bps: u32) admin function to configure the settlement fee (default 200 = 2%)
• Validate fee_bps is between 0 and 1000
• In settle_invoice, compute the fee as repayment_amount * fee_bps / 10000 and transfer it to the treasury
• Distribute repayment_amount minus the fee pro-rata to investors
• Emit a fee_collected event with the fee amount and treasury address

Acceptance Criteria

• Fee deducted from repayment before investor distribution
• Fee transferred to treasury address correctly
• fee_bps above 1000 panics with FeeTooHigh
• Non-admin caller on set_settlement_fee panics with Unauthorized
• fee_collected event emitted with correct amount

ETA: 24 hours

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Coordinate on Telegram

[AvatarMiiDe]

@AvatarMiiDe has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I understand the requirements and can deliver a clean, correct output within the expected timeframe. Kindly proceed with my assignment.

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[The-Big-Danny]

@The-Big-Danny has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

hello maintainer, i'd love to work on this issue! please assign me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @The-Big-Danny to this issue.

[drips-wave]

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