feat(examples): add doc-orphan-detector caller template

[ArchonVII]

Summary

Add the examples/doc-orphan-detector.yml caller template for the reusable doc-orphan-detector.yml (shipped in #45). Consuming repos copy it to .github/workflows/ to schedule the doc-sweep §4.7 backstop. This is what archon-setup snapshots (copyFrom: examples) to offer the cron opt-in.

Acceptance Criteria

• examples/doc-orphan-detector.yml: scheduled + workflow_dispatch caller uses: the reusable @v1, least-priv permissions (contents: read, issues: write), commented inputs.
• actionlint clean.

Related

Follow-up to #45 (the reusable). Unblocks the archon-setup agent-workflow.doc-orphan-detector cron opt-in feature.