feat(release): build and publish EPUB artifacts per language (#54)

Extend the release workflow to build separate EPUB artifacts for en, vi,
and zh in parallel via a matrix job, then publish all built files under
a single GitHub Release. Using fail-fast: false so a failure in one
language does not block releasing the others.

Also refactor build_epub.py to drive language-specific paths, filenames,
and titles from a mapping, and add zh support (title/subtitle + choice).

.github/workflows/release.yml

@@ -7,9 +7,14 @@ on:
 
 jobs:
   build:
+    name: Build EPUB (${{ matrix.lang }})
     runs-on: ubuntu-latest
-    permissions:
-      contents: write
+    strategy:
+      # Don't cancel other languages if one fails — we still want to release
+      # whichever languages built successfully.
+      fail-fast: false
+      matrix:
+        lang: [en, vi, zh]
 
     steps:
       - uses: actions/checkout@v4
@@ -25,11 +30,51 @@ jobs:
       - name: Install Mermaid CLI
         run: npm install -g @mermaid-js/mermaid-cli
 
+      - name: Install Python dependencies
+        run: |
+          uv venv
+          uv pip install -r scripts/requirements-dev.txt
+
       - name: Build EPUB
-        run: uv run scripts/build_epub.py
+        run: |
+          echo '{"args":["--no-sandbox","--disable-setuid-sandbox"]}' > /tmp/puppeteer-ci.json
+          uv run scripts/build_epub.py \
+            --lang ${{ matrix.lang }} \
+            --puppeteer-config /tmp/puppeteer-ci.json
+
+      - name: Upload EPUB artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: epub-${{ matrix.lang }}
+          path: claude-howto-guide*.epub
+          if-no-files-found: error
+          retention-days: 7
+
+  release:
+    name: Publish GitHub Release
+    needs: build
+    # Release even if some language builds failed — we still publish the
+    # artifacts that did build. `needs.build.result != 'cancelled'` guards
+    # against manually cancelled runs.
+    if: ${{ always() && needs.build.result != 'cancelled' }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+
+    steps:
+      - name: Download all EPUB artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: dist
+          pattern: epub-*
+          merge-multiple: true
+
+      - name: List built artifacts
+        run: ls -lh dist/
 
       - name: Create Release
         uses: softprops/action-gh-release@v2
         with:
-          files: claude-howto-guide.epub
+          files: dist/*.epub
           generate_release_notes: true
+          fail_on_unmatched_files: true