Fix catalog book links and rewrite PDF destinations to live HTTPS.

Module and model book cards now point at generated index.html/index.pdf
instead of directory URLs that 404. WeasyPrint file:// annotations are
mapped to https://zapier.georgelambert.org/ paths that exist. Developer
module, architecture, and research snapshot links target published files.

scripts/pdf-links.lua

@@ -11,8 +11,9 @@ function Link(el)
   if not path then
     path, frag = t, ""
   end
-  if path:match("%.md$") or path:match("%.html$") then
-    path = path:gsub("%.md$", ".pdf"):gsub("%.html$", ".pdf")
+  -- PDFs should follow other PDFs for markdown sources. Keep .html (indexes, sphinx).
+  if path:match("%.md$") then
+    path = path:gsub("%.md$", ".pdf")
     el.target = path .. frag
   end
   return el