Add structured log event for protocol fee recipient update by admin

[Chucks1093]

Summary

When the admin updates the protocol fee recipient address, there is no observable event for off-chain monitors to react to. A contract event should be emitted on each successful update so indexers can maintain an accurate record of the current fee recipient without polling storage.

Scope

• Emit a contract event on set_protocol_fee_recipient with fields: old_recipient, new_recipient, updated_at_ledger
• Use a dedicated event topic distinct from buy/sell/TTL events
• Add a test asserting the event is present in the transaction result after a successful admin update

Acceptance Criteria

• Event emitted on each successful fee recipient update
• Event contains old_recipient, new_recipient, updated_at_ledger
• Topic is distinct from other contract events
• Test confirms event presence after admin call

ETA: 12 hours

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Coordinate on Telegram

[Stephen8910]

Hello maintainer, I can work on this issue please assign

[Bilalishaq7]

Hello Maintainer good day
I can fix this and I'll submit a PR shortly after assignment

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #561)
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[grantfox-oss]

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

@Bilalishaq7's PR #591 was approved and merged by @Chucks1093.

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👏 Great work, @Bilalishaq7! Keep contributing to accesslayerorg.