Create an internal Telegram campaign for existing private chats

Requires an explicitly issued campaign-scoped key, the REST, Campaigns, scoped-routing and independent campaign-mutation feature gates, the exact campaign user allowlist, the exact campaign workspace allowlist, and Idempotency-Key (bound to this exact payload). Recipients must be existing private chats of READY internal Telegram accounts in the key workspace (max 100; duplicates collapse). No @username resolution, attachments, client-supplied names, broadcasts, or Unipile fallback. Names/usernames for personalization come from Telegram. Suppressed recipients reject the whole request. Campaign, steps and recipients are written in one database transaction; this endpoint never sends a message — the durable worker dispatches queued recipients. Ambiguous outcomes are never retried.