Rebuild the AI topic plan across the campaign's steps

Rebuilds the AI topic plan across the campaign's ai_generated steps in one pass, so the sequence reads as one narrative instead of a set of independently written steps. Manual steps are left alone, which is why regeneratedStepCount can be smaller than totalStepCount. It rewrites step topics and titles only - queued sends already created are not rewritten. Only the token owner's own campaigns can be regenerated: a campaign delegated to you, one shared by your team's visibility settings, and a deleted one all answer 404. Rate limit: this endpoint has a tighter cap of 10 requests/minute and 100/day, applied inside the shared campaigns bucket of 30 requests/minute and 1,000/day per token owner (shared by every campaign, scheduled-send, campaign-template and knowledge-hub endpoint).

Errors:

• 404 CAMPAIGN_NOT_FOUND — No campaign with this id exists, it belongs to another account (including a campaign delegated to you or shared by your team's visibility settings), or it has been deleted.
• 422 VALIDATION_FAILED — campaignId is not a 24-character hex id.
• 429 RATE_LIMITED — Either this endpoint's own cap (10 requests/minute, 100/day) or the shared campaigns bucket (30/minute, 1,000/day for this token owner, shared by every /business/campaigns, /business/scheduled-sends, /business/campaign-templates and /business/knowledge-hubs call) was exceeded. The RateLimit-* headers on the response describe the shared bucket, so a refusal from this endpoint's own cap can still report requests remaining and carries no Retry-After.
• 500 UNEXPECTED_ERROR — Topic generation failed; the detail stays in our logs.

Requires one of the following token scopes: campaigns.