feat: add retry UI for failed transactions

[bamiebot-maker]

Summary

• add a reusable TransactionRetryNotice component for failed transaction states
• update the current purchase flow to surface a clear failed state with explanatory retry messaging
• keep the retry action pattern reusable for future Stellar-related transaction flows
• reflect pending state on the action button while the transaction is processing

Testing

• git diff --check

Notes

• this clone did not have dependencies installed, so pnpm lint and pnpm build were not run locally

Closes #24

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