feat(generator): skip duplicate books when Sefaria version exists

[kdroidFilter]

Summary

• Add deduplication logic in Otzaria generator to prioritize Sefaria source
• When a book with the same heRef already exists from Sefaria, skip insertion from other sources

Changes

• Check for existing book by heRef before inserting in Otzaria generator
• If existing book is from Sefaria source, skip the duplicate

Test plan

• Build SeforimLibrary: ./gradlew :SeforimLibrary:build
• Regenerate database and verify no duplicates from Sefaria exist