A repayment cannot be charged back, so a mistaken payment on a closed loan can only be corrected outside this app

## What is missing

Fineract accepts `chargeback` against an individual loan transaction. It reverses a repayment and, where that repayment had closed the loan, reopens it — the correction path for a payment applied in error or later dishonoured. This app offers no way to invoke it.

Confirmed against a running `apache/fineract`, using the discriminator established in #268 — an unrecognised command answers `error.msg.query.parameter.value.unsupported` on the `command` parameter, exactly as an invented name does:

| Probe | Result |
|---|---|
| `POST /loans/{id}/transactions?command=totallyNotACommand` | `error.msg.query.parameter.value.unsupported` — **unrecognised** (control) |
| `POST /loans/{id}/transactions?command=writeoff` | `validation.msg.loan.transaction.transactionDate.cannot.be.blank` — **recognised** (control, and the app wires this one) |
| `POST /loans/{id}/transactions?command=chargeback` | `error.msg.query.parameter.value.unsupported` — **unrecognised at this level** |
| `POST /loans/{id}/transactions/{transactionId}?command=chargeback` | `validation.msg.loan.transaction.transactionAmount.cannot.be.blank` — **recognised** |

That last pair is the important detail: **chargeback is only accepted against a specific transaction**, not at loan level. So it does not belong on the loan's Actions menu with the other commands — it belongs as a row-level action on the Transactions tab, next to the repayment being reversed, which is also how a user would think about it.

## What the UI offers today

Against a real Active loan seeded into a local Fineract stack, the Transactions tab's only affordances are the shared Repayment / Actions / Back controls — there is no per-row action at all:


`grep -rli chargeback src/app` returns nothing outside the generated API client. The client method already exists:

```ts
loanTransactionsService.postLoansLoanIdTransactionsTransactionId(loanId, transactionId, request, 'chargeback')
```

The platform permission is `CHARGEBACK_LOAN` (confirmed present in `GET /permissions`), so the action can be gated with `appRequiresPermission` like every other command on this screen.

## Suggested scope

A row-level action on the Transactions tab, offered only on rows that can actually be charged back (a repayment-type transaction that has not already been reversed), collecting `transactionAmount` and a payment type. The request body is:

```ts
{ transactionAmount: number, locale: string, paymentTypeId?: number }
```

Fineract ships "Repayment Adjustment: Chargeback" and "Repayment Adjustment: Refund" payment types for exactly this.

## Why it is worth doing

A repayment recorded against the wrong loan, or one whose cheque later bounces, has no correction path in this app once it has closed the loan. The alternative is editing the platform outside the UI, which leaves the back office unable to complete a routine correction on its own.

## Environment

`main` at `7c51d90b`. Probes against `apache/fineract` running locally via `deploy/docker-compose-e2e.yml`; screenshot from a loan seeded with the repository's own `e2e/utils/seed-api.ts` helpers.

Start at the loan Transactions tab implementation and its existing Repayment or Actions controls, then inspect the generated loanTransactionsService method and the appRequiresPermission pattern. Add the row-level chargeback flow for eligible repayment transactions, including amount and payment type, and verify that CHARGEBACK_LOAN permission gating and the chargeback request work as described.

Written by the indexing model from the issue text.