Migrate campaign labels from campaign:<id> to z_campaign_<id> format

[Copilot]

Campaign labels used the legacy campaign:<id> format. Go code already used z_campaign_<id>, but JavaScript code and documentation still referenced the old format. The z_ prefix ensures campaign labels sort last in GitHub's label lists.

Changes

JavaScript implementation:

• Centralized prefix in CAMPAIGN_LABEL_PREFIX = "z_campaign_" constant
• Added formatCampaignLabel() helper mirroring Go's pkg/stringutil/identifiers.go:FormatCampaignLabel()
• Removed legacy GH_AW_TRACKER_LABEL environment variable support

Code example:

// Before
labels: [`campaign:${campaignId}`]

// After
const CAMPAIGN_LABEL_PREFIX = "z_campaign_";
function formatCampaignLabel(campaignId) {
  return `${CAMPAIGN_LABEL_PREFIX}${String(campaignId).toLowerCase().replace(/[_\s]+/g, "-")}`;
}
labels: [formatCampaignLabel(campaignId)]

Tests & documentation:

• Updated 8 test expectations across 3 test files
• Updated campaign specs, examples, and safe-outputs reference documentation
• Updated comment in pkg/workflow/safe_output_validation_config.go

Notes

Go validation already rejects campaign: format. This PR completes the migration by aligning JavaScript and documentation with the established convention.

Original prompt

Catch and remove all legacy label references in campaign related code campaign:<id> and replace with new convention z_campaign_<id>. Make it robust and consider outsourcing in a campaign prefix variable or similar.

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