The reference footer was anchored to a fixed position near the bottom
margin, causing it to overlap with notes text on songs that had both
notes and references (e.g., "Die Gedanken sind frei").
Changed renderReferenceFooter to use flow-based positioning from the
current y-position after notes/metadata, ensuring the separator line,
abbreviation headers, and page numbers always render below the
preceding content without overlap.
Also updated calculateFooterReservation and MeasurementEngine to match
the simplified layout calculation, and added toc.highlight_column to
the example songbook.yaml to demonstrate column highlighting.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
