Clarify tracker-id is optional for campaign worker workflows

[Copilot]

Campaign worker workflows do not require tracker-id - campaigns discover workers via labels. Documentation incorrectly implied it was mandatory.

Changes

• Documentation: Updated worker workflow pattern to indicate tracker-id is optional

  • Changed "should include tracker-id" → "optionally include tracker-id in frontmatter"
  • Clarified campaigns discover via labels (primary), cache-memory, or tracker-id search (fallback)

• Test: Added TestFuseWorkflowWithoutTrackerID verifying fusion succeeds without tracker-id

Context

Campaign discovery supports multiple methods:

# Primary: Campaign-specific labels
label: "z_campaign_security-audit"

# Secondary: Generic campaign label  
label: "agentic-campaign"

# Fallback: tracker-id search (optional)
tracker-id: "security-scanner"  # Not required

The extractTrackerID function already returns empty string when absent - no validation enforces its presence.

Original prompt

Don't require a tracker-id for campaign worker workflows

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