Add creators to campaign

Add creators to a campaign, as Add to campaign on the Creators tab does. A draft only grows its audience (nothing sends until launch). An active or paused campaign ENROLS them now: only creators with a REVEALED email that never opted out or bounced; the rest come back as excluded (dm_only have no email at all). Enrolled creators get the campaign's first email on the engine's schedule, window and daily cap. Campaigns written for websites refuse creators. Guarded: without approval_token it returns {error:"approval_required", approval_token, summary} for the user to confirm; call again with the token. Every dashboard guardrail still applies: this is exactly what a user clicking the dashboard could do, no more. GUARDED: requires the account's Unrestricted MCP setting; returns 403 {error:'restricted'} otherwise.