Pre-install popular Quarto extensions in the Docker image

Dockerfile-base: after Quarto is installed, run 'quarto add --no-prompt'
  for a curated set of extensions into /opt/quarto-extensions/. Quarto
  writes _extensions/<author>/<name>/ in the working dir, giving us a
  clean shared store. Extensions included:
    - igorlima/charged-ieee      — IEEE paper format (Typst)
    - quarto-ext/fontawesome     — Font Awesome icons
    - quarto-ext/attribution     — attribution footer on RevealJS slides
    - quarto-ext/pointer         — laser pointer for presentations
    - quarto-ext/drop            — drop-down overlay for RevealJS
  Adding more: one extra '&& quarto add --no-prompt <author>/<repo>' line.

QuartoRunner: before quarto render, merge /opt/quarto-extensions/_extensions/
  into the compile dir's _extensions/ with 'cp -rn' (no-clobber). This
  makes all pre-installed extensions available to every project without
  any user action. Project-uploaded _extensions/ files take precedence
  since cp -n never overwrites existing files.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server-ce/Dockerfile-base

@@ -44,6 +44,27 @@ RUN curl -fsSL "https://github.com/quarto-dev/quarto-cli/releases/download/v${QU
 &&  mkdir -p /var/www/.cache/quarto \
 &&  chown -R www-data:www-data /var/www/.cache
 
+# Pre-install popular Quarto extensions
+# -----------------------------------------------------------------------
+# Extensions land in /opt/quarto-extensions/_extensions/<author>/<name>/.
+# QuartoRunner copies them into each project's compile dir (no-clobber,
+# so user-uploaded extensions in their project always take precedence).
+# To add more: append another line:  && quarto add --no-prompt <author>/<repo>
+# -----------------------------------------------------------------------
+RUN mkdir -p /opt/quarto-extensions \
+&&  cd /opt/quarto-extensions \
+    \
+    # Typst document formats
+&&  quarto add --no-prompt igorlima/charged-ieee \
+    \
+    # RevealJS presentation plugins (official Quarto extensions)
+&&  quarto add --no-prompt quarto-ext/fontawesome \
+&&  quarto add --no-prompt quarto-ext/attribution \
+&&  quarto add --no-prompt quarto-ext/pointer \
+&&  quarto add --no-prompt quarto-ext/drop \
+    \
+&&  chown -R www-data:www-data /opt/quarto-extensions
+
 
 # Set up overleaf user and home directory
 # -----------------------------------------