## Summary
- Adds `banking:backfill-ibans` artisan command to backfill null `iban`
values on Enable Banking accounts by calling `GET /accounts/{uid}` for
each affected account.
- Adds `getAccount()` to `BankingProviderInterface` and
`EnableBankingProvider`.
- 9 feature tests covering all paths: happy path, no-IBAN skip, dry-run,
user/connection filters, API failure handling.
## Why
Accounts connected before
[#220](https://github.com/whisper-money/whisper-money/pull/220) was
deployed have `null` IBANs. Without IBANs, reconnects fall back to
positional matching which is less reliable. Running this command once in
production populates the IBAN for all existing accounts so future
reconnects use the safer IBAN-based strategy.
## Usage
```bash
# Dry run first
php artisan banking:backfill-ibans --dry-run
# Run for all accounts
php artisan banking:backfill-ibans
# Scope to a specific user or connection
php artisan banking:backfill-ibans --user=user@example.com
php artisan banking:backfill-ibans --connection=<connection-id>
```
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