feat: documents to PDF

[Chimi6]

Step 1 of documents to PDF (temp plan): base-14 fonts.

• src/io/pdf/compose.rs: an event sink that sets any reader's Markdown event stream on Letter pages with one-inch margins: headings, paragraphs broken first fit on AFM widths, nested bullet and numbered lists, block quotes, code blocks, tables (content widths, wrapping, alignment, grid), rules, links (URI annotations), footnotes; a page is written when full.
• PdfDocument::text_page, base-14 font resources, link annotations, /Info title.
• Converters markdown/html/text/docx/pages -> pdf.
• Tests (tests/to_pdf.rs): Markdown round-trips through PDF and our reader unchanged; a long document keeps every word inside the margins; links; WinAnsi losses; every document format reaches PDF. All Pages and Word fixtures convert and read/render in poppler without errors.
• Size budgets raised 2.55 -> 2.70 MB (binary) and 1.30 -> 1.40 MB (wasm); binary 2,601,232, wasm 1,298,229.
• STATE records the owner's font decision (system fonts, nothing bundled).