fix: add SHA256 checksums to prebuilt archives and retain LICENSE

Generate .sha256 checksum files alongside each prebuilt tarball for
download integrity verification. Stop stripping the LICENSE file from
archives to comply with AGPL-3.0 distribution requirements.

.github/workflows/release.yml

@@ -111,7 +111,7 @@ jobs:
           rm -rf tests .github .husky scripts
           rm -rf .releaserc.json biome.json .editorconfig .gitattributes
           rm -rf .git .gitignore
-          rm -f CHANGELOG.md LICENSE README.md CONTRIBUTING.md SECURITY.md
+          rm -f CHANGELOG.md README.md CONTRIBUTING.md SECURITY.md
 
           ARCHIVE_NAME="snapotter-v${VERSION}-linux-${ARCH}.tar.gz"
           cd ..
@@ -123,11 +123,14 @@ jobs:
           echo "archive_name=${ARCHIVE_NAME}" >> "$GITHUB_ENV"
           echo "Archive: ${ARCHIVE_NAME} ($(du -sh /tmp/${ARCHIVE_NAME} | cut -f1))"
 
+      - name: Generate checksum
+        run: cd /tmp && sha256sum "${archive_name}" > "${archive_name}.sha256"
+
       - name: Upload to GitHub Release
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           VERSION: ${{ needs.release.outputs.new_version }}
-        run: gh release upload "v${VERSION}" "/tmp/${archive_name}" --clobber
+        run: gh release upload "v${VERSION}" "/tmp/${archive_name}" "/tmp/${archive_name}.sha256" --clobber
 
   docker:
     name: Build (${{ matrix.platform }})