Contracts: Emit Soroban events for Korean debt yield accrual

[Junirezz]

Context

deposit and withdraw publish Soroban events for indexer consumption, but accrue_korean_debt_yield mutates VaultState.total_assets without emitting an event.

Problem / Gap

Off-chain APY dashboards and the backend indexer cannot observe Korean sovereign-debt yield harvests, creating a blind spot between on-chain yield and share-price increases.

Proposed approach

• Publish an event (e.g., (symbol_short!("k_yield"),)) with (harvested_amount, new_total_assets) after successful harvest.
• Mirror event schema in event_tests.rs and document payload for backend consumers.

Files/areas affected

• contracts/vault/src/lib.rs (accrue_korean_debt_yield)
• contracts/vault/src/event_tests.rs

[OsejiFabian]

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PLEASE I WOULD LIKE TO WORK ON THIS ISSUE

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[Amas-01]

@Amas-01 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Maintainer
I'll like to work on this Issue. Please Assign me

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[Devsol-01]

@Devsol-01 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Please can i be assigned this issue

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