fix(maintenance-pool): restore balance on failed escrow withdrawal (#459)

[Proxima84-code]

Resolves #459.

Root Cause

In MaintenancePoolService.assignReward(), the pool balance is atomically decremented in PostgreSQL before executing escrowService.poolWithdraw(). If the on-chain Soroban withdrawal fails (RPC simulation failure, recipient mismatch, or payment record persistence error), the deducted amount was never restored. This resulted in permanent database balance drift against the actual contract balance.

Fix

• Wrapped escrowService.poolWithdraw() in a try/catch block.
• Implemented a compensating transaction via this.poolRepo.increment({ id: pool.id }, 'balance', Number(amount)) on error before rethrowing the original exception.
• Added a regression test ensuring pool balance restoration when poolWithdraw rejects.
• Verified test suite: 17/17 tests passing.

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[Proxima84-code]

Hi @maintainers,

Since the deadline for issue #459 passed on September 30 without a solution from the original assignee, I have submitted a complete and verified fix here (all 17 unit tests passing, clean TypeScript build).

Could you please approve the CI workflow run and review the PR? Thank you!