slides: fix title page spacing, enable LIP6 and Sorbonne

- Reserve a left margin in the partner logo grid so a full grid stays
  clear of the affiliations.
- Let the space above the title shrink when the title page overflows,
  so the logos keep a bottom margin equal to the side margins.
- Enable the LIP6 and Sorbonne Université partners in the example deck.
- Note that author and institute blocks must stay plain: table and
  flushleft wrappers add vertical space.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Slides/slides.tex

@@ -10,14 +10,17 @@
 \partner{ubo}
 \partner{ensta}
 % \partner{ifremer}
-% \partner{lip6}
-% \partner{sorbonne}
+\partner{lip6}
+\partner{sorbonne}
 % \partner{academia-sinica}
 % \partner{taipei}
 % See README.md for supported formats and custom logo paths.
 % Optional legacy title graphic (used only when no partners are enabled):
 % \titlegraphic{\flushright\includegraphics[height=1.3cm]{img/logos.png}\vspace{.5cm}}
 
+% Keep author and institute blocks plain: table or flushleft wrappers add
+% vertical space, which pushes the title up and misaligns the affiliations
+% with the partner logos.
 \author{
     \texorpdfstring{
         \begin{tabular}{@{}l@{}}