* Make xhtml2pdf optional, fix install on Linux without libcairo
Move xhtml2pdf to the new [pdf] extra so default `pip install maigret`
no longer pulls pycairo (which has no Linux/macOS wheels and breaks the
build without libcairo2-dev). save_pdf_report now raises a clear
RuntimeError pointing to `pip install 'maigret[pdf]'`, and the CLI
turns it into a friendly warning instead of a crash. Adds tests
covering the missing-extra path, plus per-OS install docs.
Fix for #2657, #2534
* Make arabic-reshaper and python-bidi optional; idempotent update of db_meta.json and sites.md
* Regenerated poerty.lock
* Update CI workflow to cover minimal installation without PDF deps
