Implement highlighted PDF packet export

[Xyloth]

Generate issue packets with highlighted source pages, cover sheets, quote lists, exhibit indexes, and ZIP/PDF export paths suitable for attorney, mediation, complaint, or board packets.

[Xyloth]

Pressure test confirms highlighted packet export depends on source-page geometry, not just quote text. For OCR/scanned inputs, export needs rendered page images/PDF pages, highlight rectangles, page references, and a fallback quote sheet when exact coordinates are not yet human-confirmed.