FullbookTranslate v0.5.0 — case-first success library

This release reorganizes FullbookTranslate around readable, complete whole-book translation cases.\n\n- Groups cases by format, language pair, and book title.\n- Places downloadable source and translated EPUB files side by side.\n- Shows processing time, content size, structure checks, Codex review, and honest limitations.\n- Removes source-only probes and public engineering execution directories.\n- Publishes only two verified complete CJK-to-English success cases: Rashomon and A Madman's Diary.\n\nRun \python scripts/validate_repo.py\ to verify case contracts, file hashes, rights metadata, and EPUB containers.