Fix #423: publish a standalone Linux CLI archive (#613)

On Linux, pdfcraft-cli shipped only inside the desktop packages (about
55 MB), while macOS already publishes pdfcraft-cli-<v>-macos-universal.zip.
Servers, CI and agent sandboxes only need the headless CLI.

packaging/linux/package.sh gains a `cli` format, on by default, that writes
pdfcraft-cli-<v>-linux-<arch>.tar.gz: the stripped pdfcraft-cli from the
shared staging tree plus the licences/README via copy_docs. copy_docs now
also copies NOTICE (every package benefits). The release job already
uploads and checksums every file in dist/release; its package check now
lists the archive and runs the extracted binary. README and
docs/releasing.md list the new artifact and state the glibc 2.35 baseline.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -213,7 +213,7 @@ jobs:
       - name: Apply version override
         if: inputs.version != ''
         run: cargo xtask version set "$PDFCRAFT_VERSION"
-      - name: Build and package (AppImage, deb, rpm, tar.gz)
+      - name: Build and package (AppImage, deb, rpm, tar.gz, CLI tar.gz)
         env:
           CRAFT_FONTS_DIR: ${{ github.workspace }}/craft-fonts
           CRAFT_FONTS_REQUIRED: "1"
@@ -223,6 +223,12 @@ jobs:
           dpkg-deb --info dist/release/*.deb
           dpkg-deb --contents dist/release/*.deb | grep -E 'usr/bin/pdfcraft$|metainfo|applications'
           ldd target/release/pdfcraft
+          # The CLI-only archive: the binary and its licences, and it runs.
+          cli="dist/release/pdfcraft-cli-$PDFCRAFT_VERSION-linux-${{ matrix.arch }}.tar.gz"
+          tar -tzf "$cli" | grep -E '/pdfcraft-cli$'
+          tar -tzf "$cli" | grep -E '/LICENSE-APACHE$'
+          mkdir -p "$RUNNER_TEMP/cli" && tar -xzf "$cli" -C "$RUNNER_TEMP/cli"
+          "$RUNNER_TEMP/cli/pdfcraft-cli-$PDFCRAFT_VERSION-linux-${{ matrix.arch }}/pdfcraft-cli" --version
           python3 -c "import yaml; m = yaml.safe_load(open('packaging/linux/flatpak/ai.storyteller.pdfcraft.yml')); assert m['id'] == 'ai.storyteller.pdfcraft'"
           for appimage in dist/release/*.AppImage; do
             chmod +x "$appimage"