fix: add campaign label handling

[mnkiefer]

• Fixes campaign discovery returning 0 items and ensures campaign workers’ outputs are always discoverable.
• Centralizes campaign label injection in the safe-output dispatcher: when GH_AW_CAMPAIGN_ID is present, create_issue] and create_pull_request messages automatically get agentic-campaign and z_campaign_ (plus optional tracker label) before dispatch.
• Propagates campaign context into safe-output jobs by exporting GH_AW_CAMPAIGN_ID from repo-memory campaign-id, so workers don't need to manually add labels.