@spec get(Plug.Conn.t(), String.t()) :: Plug.Conn.t()

Handles GET /api/v2/campaigns/:id - Get a campaign by ID.

@spec set_status(Plug.Conn.t(), String.t()) :: Plug.Conn.t()

Handles POST /api/v2/campaigns/:id/set-status - Change a campaign's status.

Validates the requested status against the OpenAPI Campaign.status enum, updates the campaign in the DB, and enqueues a campaign_status_change webhook event.

Mirrors the real CampaignFlow API: returns the updated Campaign on success, 422 if the status value is invalid, 404 if the campaign doesn't exist.