ids theme: rework the references slide layout and auto-fit it

Address four points of criticism on the bibliography slide:
- "Authors (Year):" no longer sits bold on its own line but runs
  inline in a medium weight -- it was overemphasized for text that is
  already darker than the entry, and looked blurred at small sizes.
- Entries get breathing room below the title bar (padding, so the
  vertical-centering wrapper's first-child margin reset cannot eat it).
- Authors running inline saves a line per entry.
- The slide auto-fits: decreasing font sizes are tried and, when even
  the smallest would overflow, trailing entries move onto
  automatically created "References (cont.)" slides (Reveal.sync()
  registers them, so navigation, menu and numbering keep working).
  In print/PDF the scroll box is disabled so long bibliographies flow
  across pages instead of being clipped.

Change-Id: I59897723d9eabe824f7f5ed794cf75c0082e031b
diff --git a/.gitignore b/.gitignore
index fe7ddc6..ad16f6d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,4 @@
 .sass-cache/
 examples/#references.bib#
 examples/@inproceedings{kupietz-deliko2026,
+/Quantitative*.pdf