feat: implement Stripe transaction history and refund functionality f…

[Berny-ft]

Closes #89

Overview

Admins can view a customer’s Stripe charge history and issue full or partial refunds directly from the Users table, without leaving the app.

Backend (actions.ts, schema.ts)

getUserTransactions — lists charges for a Stripe customer with cursor pagination (starting_after / ending_before), expanded refunds and payment intents, and mapped descriptions from charge / PI / metadata.
createTransactionRefund — creates refunds via Stripe with idempotency keys, admin auth, server-side refundable balance checks, and returns the updated charge for the UI.
Zod schemas for list params and refund payloads.
UI (user-transactions-modals.tsx, user-actions-cell.tsx)

Receipt icon on each user row (when they have a stripeCustomerId) opens a transactions modal.
Paginated table: date, description, amount, refund status.
Row click opens a refund dialog with refund history, partial amount input, and confirm-before-submit for full/partial refunds.
Toast feedback for success, pending, and error states.

Testing

Unit tests (actions.test.ts)

getUserTransactions: admin guard, charge mapping from Stripe list response.
createTransactionRefund: unauthorized, fully refunded charge, over-cap partial, successful full refund with updated transaction.

Screenshots / Screencasts

Checklist

• Code is neat, readable, and works
• Code is commented where appropriate and well-documented
• Commit messages follow our guidelines
• Issue number is linked
• Branch is linked
• Reviewers are assigned (one of your tech leads)

Notes

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[martin0024]

good pr berny