Fix catalog PDF links; add bring-online guide; feature zappier billing

PDFs rewrite in-document .md/.html links to sibling PDFs. Catalog
start page is GETTING-STARTED (install, first-up, monitor). Billing
and user platform is zappier-edge (original ~/zappier tree).

scripts/build-readme-latex.py

@@ -48,6 +48,7 @@ def main() -> None:
             "--metadata=title=Verae Time × Zapier — repository READMEs",
             f"--include-in-header={hdr}",
             "--syntax-highlighting=breezedark",
+            f"--lua-filter={ROOT / 'scripts' / 'pdf-links.lua'}",
         ],
         check=True,
     )