Emojis in exported PDFs no longer render as empty "tofu" boxes. The default WeasyPrint stylesheet now lists ``"Noto Color Emoji"`` (with ``"Noto Emoji"`` as a monochrome fallback and ``"Segoe UI Emoji"`` / ``"Apple Color Emoji"`` for native installs) at the tail of both the body and ``code``/``pre`` font-family stacks, and the official Docker image now bundles ``fonts-noto-color-emoji`` alongside ``fonts-noto-cjk``. Non-Docker users on Linux without an emoji font installed still need to install one (e.g. ``apt install fonts-noto-color-emoji``) — see ``docs/faq.md``. This change also fixes a pre-existing flaw in the ``custom_css`` path: ``markdown_to_pdf(custom_css=...)`` previously *replaced* the default stylesheet entirely, silently dropping the CJK fallback from #4055; it now layers custom CSS on top of the default so the font fallbacks survive.
