Telegram grants: show expired/revoked history and add expiry reminders #74

Context

src/features/telegram/grants-page.tsx (/dashboard/telegram/grants) currently only shows two views, backed by context.backend.tg.grants.getOngoing and .getScheduled:

• Ongoing — grants currently in effect
• Scheduled — grants that will start in the future

There is no way to see grants that have ended (naturally expired, or revoked/interrupted early), and no reminder when an active or scheduled grant is about to expire. This is called out explicitly in PRD_Classificazione_Feature.md §11 ("Telegram grants: storico dei grant terminati/interrotti; reminder sulle scadenze imminenti") as a low-effort improvement to an area that's already in production — no new roles/permissions/Identity Provider work needed, it only touches this existing page and its backend endpoints.

Problem

• Once a grant's validUntil passes (or it's revoked before that), it disappears from the dashboard entirely. There's no audit trail visible to Direttivo/owners of who was authorized to bypass moderation, for how long, and whether it ran its full course or was cut short.
• Nobody is notified before a grant is about to expire, so an authorization can lapse silently (e.g. a partner association mid-campaign) with no chance to renew it in time.

Proposed changes

1. Grant history / expired tab
   • Add a getExpired (or getHistory) backend query alongside the existing getOngoing/getScheduled, returning grants whose validUntil is in the past, plus a way to distinguish "ran to term" vs "revoked early" if that's tracked (if not currently tracked, this may need a revokedAt/endedEarly flag — check Moderation/grants schema in the telegram bot repo, which is presumably the source of truth for this table).
   • Add a third tab ("Expired"/"Past") to the ToggleGroup in grants-page.tsx, next to "Ongoing" and "Scheduled", following the same table/column pattern already used.