Fix TeX Live install: texcount is not a standalone package

The base image build failed with "E: Unable to locate package texcount".
texcount ships inside texlive-extra-utils, not as its own apt package.
Replace the bogus texcount entry with texlive-extra-utils (which provides
both texcount and latexmk). latexmk is kept explicit for clarity.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server-ce/Dockerfile-base

@@ -86,7 +86,7 @@ RUN apt-get update \
       | xargs apt-get install -y --no-install-recommends \
 &&  apt-get install -y --no-install-recommends \
       texlive-xetex texlive-luatex texlive-bibtex-extra biber \
-      latexmk texcount chktex fontconfig inkscape python3-pygments \
+      texlive-extra-utils latexmk chktex fontconfig inkscape python3-pygments \
 &&  rm -rf /var/lib/apt/lists/*