fix: provide --source + --data (empty TTS config) for epub3-to-pef

DAISY Pipeline epub3-to-pef requires both --source (EPUB input) and --data
(TTS config file) even for braille-only conversion. Providing a minimal
empty TTS config to satisfy the requirement.

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

Author: taylorarndt

.github/workflows/build-epub.yml

@@ -57,8 +57,11 @@ jobs:
         continue-on-error: true
         run: |
           mkdir -p epub/brf
+          # Create a minimal TTS config (required by DAISY Pipeline even for braille scripts)
+          echo '<?xml version="1.0" encoding="UTF-8"?><config></config>' > /tmp/tts-config.xml
           pipeline2/daisy-pipeline/cli/dp2 epub3-to-pef \
-            --data "$(pwd)/epub/git-going-with-github.epub" \
+            --source "$(pwd)/epub/git-going-with-github.epub" \
+            --data /tmp/tts-config.xml \
             --output "$(pwd)/epub/brf/" \
             --output-file-format "(-daisy-locale: en-US)" || echo "BRF conversion failed - check dp2 logs above"
           ls epub/brf/ || echo "No BRF output produced"