chore: update campaign docs

[mnkiefer]

• Standardizes the campaign tracking label format across docs,from campaign:<id> to z_campaign_<id>
• Updates the campaign orchestrator execution model and clarifies the separation of responsibilities between orchestrators and workers.

[mnkiefer]

@copilot fix docs build

[Copilot]

@mnkiefer I've opened a new pull request, #11904, to work on those changes. Once the pull request is ready, I'll request review from you.