chore: bump version to 1.4.0

[Harsh-2002]

Cuts 1.4.0. Everything since 1.3.0 is PDF export work.

	1.3.0	1.4.0
README → PDF	3,042,754 B	200,810 B
same input, exported twice	different bytes	byte-identical
**bold** / *italic*	rendered as regular text	render correctly
tests	298	324

• refactor(pdf): drop markdown2pdf, call genpdfi and printpdf directly #9 dropped markdown2pdf — a whole markdown→PDF converter used for two font-loading calls — for 19 crates
• fix(pdf): resolve bold and italic faces instead of reusing regular #10 fixed bold and italic, which had resolved to the regular face for headings, table headers, alert titles and list bullets as well as inline emphasis
• feat(pdf): subset embedded fonts deterministically #11 subset embedded fonts deterministically, cutting 93% of file size
• fix(pdf): make export byte-reproducible #12 made export byte-reproducible and added SOURCE_DATE_EPOCH support
• perf(pdf): draw square backgrounds as vectors, not rasters #13 draw square backgrounds as vectors rather than rasterizing them
• fix(pdf): antialias panel corners and give each panel its own temp file #14 antialiased rounded corners and gave each panel its own temp file

Gate is green: fmt, clippy, 324 tests. README documents the reproducibility guarantee.