978858362d
Add the @pubscript/exporters package exporting a flattened ProseMirror project to Markdown, HTML, EPUB, DOCX, ODT and PDF, plus a deterministic generatedAt timestamp threaded through every format (ZIP entry dates, PDF /ID, DOCX dc:created/modified, EPUB id, HTML/XML footers) so golden files are byte-stable. Wire an ExportDialog into the web app (Topbar trigger, App route) with format selection, theme pick, and download helpers. Add round-trip and golden-file determinism tests (22) covering non-empty output, byte-identical re-exports, Markdown round-trip through the editor, and EPUB/ODT ZIP + mimetype + XML validation.