CI: Install Fira Sans font for consistent PNG snapshot rendering

Add step to download and install Fira Sans font in CI environment
to ensure consistent font rendering between local development and
GitHub Actions. This fixes the PNG snapshot test failures caused
by font fallback differences.

Author: Turbo87

.github/workflows/ci.yml

@@ -177,6 +177,18 @@ jobs:
           rm -rf "typst-x86_64-unknown-linux-musl" "typst-x86_64-unknown-linux-musl.tar.xz"
           typst --version
 
+      - name: Install Fira Sans font
+        run: |
+          # Download and install Fira Sans
+          wget -q "https://github.com/mozilla/Fira/archive/4.202.zip"
+          unzip -q "4.202.zip"
+          sudo mkdir -p /usr/local/share/fonts/fira-sans
+          sudo cp Fira-4.202/otf/FiraSans-*.otf /usr/local/share/fonts/fira-sans/
+          sudo fc-cache -f -v
+          rm -rf "4.202.zip" "Fira-4.202"
+          # Verify font is available
+          fc-list | grep -i "fira sans" || echo "Fira Sans not found"
+
       - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
         with:
           save-if: ${{ github.ref == 'refs/heads/main' }}