fix: drop rpm build target and stale system tool depends

- Remove rpm from linux build targets (rpmbuild not available locally)
  CI can add it back with apt-get if needed, but pandoc/ffmpeg are now
  bundled so the rpm depends were incorrect anyway
- Remove rpmbuild apt install step from release.yml (not needed)
- Remove pandoc/ffmpeg from deb depends — they are now bundled binaries
- Keep imagemagick and libreoffice-common in deb depends (not bundled)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/release.yml

@@ -19,9 +19,6 @@ jobs:
           node-version: 20
           cache: npm
 
-      - name: Install rpmbuild
-        run: sudo apt-get update && sudo apt-get install -y rpm
-
       - name: Install dependencies
         run: npm ci