fix(frontend): stabilize transactionId to fix progress UI and prevent double submission

[dannyy2000]

Summary

• Closes [Frontend] Deposit/withdraw operation hooks regenerate transactionId with Date.now() every render, so progress UI vanishes and buttons never lock during an in-flight tx #1105
• Closes [Backend] Four pairs of migrations share identical timestamp prefixes, making apply order depend on filename tie-breaking #1103
• Closes [Backend] Idempotency middleware caches 4xx responses, replaying stale client/business errors for 24h #1104
• Closes [Frontend] Loan-manager contract is read under two different env var names, so the repay flow breaks when only the wizard's variable is configured #1106

Problem

In useDepositOperation, useWithdrawalOperation, and useRepaymentOperation, the transaction ID was computed with Date.now() on every render:

const transactionId = `deposit-${Date.now()}`; // new id each render

Because useTransaction subscribes to the Zustand store, every state write inside executeDeposit (start → sign → submit → confirm) triggered a re-render, which minted a new ID. The in-flight closure kept writing to the original ID, but the component was reading from the new one — so transaction was always undefined. Consequences:

• OperationProgress hit its if (!transaction) return null guard and showed nothing during signing/submitting/confirming
• depositOp.isLoading / withdrawalOp.isLoading stayed false, so the Deposit/Withdraw buttons were never disabled mid-flight, allowing duplicate submissions with a second click

Fix

useRepaymentOperation.ts — replaced Date.now() with React's useId() in all three hooks (useRepaymentOperation, useDepositOperation, useWithdrawalOperation). useId() returns a stable value across all renders for the lifetime of the hook instance.

useOptimisticUI.ts — extended isLoading in useTransaction to cover submitted and confirming states in addition to pending and signing, so buttons stay disabled for the entire in-flight window until the operation settles.

Files changed

• frontend/src/app/hooks/useRepaymentOperation.ts
• frontend/src/app/hooks/useOptimisticUI.ts