i18n: restore {username} in unbannedUserFromCommunity (es, it, sk)

[owgreen-dev]

Pull Request Description

unbannedUserFromCommunity in es, it and sk dropped the {username} placeholder, so the snackbar can't say who was unbanned. Restored it in each, keeping the existing wording:

locale	before	after
app_es.arb	Usuario no expulsado de la comunidad	Se anuló la expulsión de {username} de la comunidad
app_it.arb	Sbanna Utente dalla Comunità	Sbannato {username} dalla comunità
app_sk.arb	Odblokovaný používateľ z komunity	Odblokovaný používateľ {username} z komunity

3 files, 3 lines; the @unbannedUserFromCommunity placeholder metadata already declares username, so flutter gen-l10n picks it up unchanged. (Not touched on purpose: the {count, plural, …} strings that several locales simplified to a single word — that's a plural-fidelity choice, not a broken variable.)

Found with an open-source i18n placeholder checker I maintain (shipi18n); each string checked by hand against app_en.arb. Full scan for this repo: https://shipi18n.com/oss#thunder

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

n/a — string-only change.

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained? — no new packages
• Did you use localized strings (and added appropriate descriptions) where applicable? — this PR is the localized strings
• Did you add semanticLabels where applicable for accessibility? — n/a