chore: comment the provenance MARKER export

[agentiknet]

Add a one-line comment directly above the MARKER export in scripts/lib/provenance-footer.mjs explaining what the marker string is used for (the native-vs-legacy footer discriminator). Trivial, comment-only change — smoke test for the PR-creation provenance footer lane.

[agentiknet]

/implement

[ponytail-coder]

Triage: Add explanatory comment above MARKER export in scripts/lib/provenance-footer.mjs.

• Type: chore
• Area: scripts (no changeset needed — scripts/** change, no package export affected)
• Actionable: yes — target confirmed at scripts/lib/provenance-footer.mjs:10
• Suggested next step: ready to implement — /implement already requested, proceeding.

[agentiknet]

Smoke-test issue for the PR-creation footer lane — verified. Closing.