feature/multiple authors per book

[codebude]

• Added support for multiple authors per book
• Clarify on author split modes in api and file import
• Mark author field as deprecated
• Joined validator for author and authors field to ensure at least one author is set
• Added different authors statistics card
• Fix docs fastdom dependency
• Export tags and authors as list instead of flattened string in user data export
• Fix inverted top/worst rated book ordering on statistics page
• Allow import transforms to return lists for adaptive authors/tags targets
• Use authors as the import target field with backward-compatible mapping
• Show authors field with adaptive string/array hint in import mapping editor
• Document authors import target and CSV export separators

[github-actions]

🧪 Test Results — 88c8963

✅ Backend (pytest) — 929 passed, 0 failed, 0 skipped (929 total)
✅ CLI (pytest) — 54 passed, 0 failed, 0 skipped (54 total)
✅ Frontend (vitest) — 405 passed, 0 failed, 0 skipped (405 total)
❌ E2E (Playwright) — 65 passed, 3 failed, 0 skipped (68 total)

Summary: 1453 ✅ passed, 3 ❌ failed (1456 total)

[github-actions]

🧪 Test Results — aa15b20

✅ Backend (pytest) — 929 passed, 0 failed, 0 skipped (929 total)
✅ CLI (pytest) — 54 passed, 0 failed, 0 skipped (54 total)
✅ Frontend (vitest) — 405 passed, 0 failed, 0 skipped (405 total)
✅ E2E (Playwright) — 68 passed, 0 failed, 0 skipped (68 total)

Summary: ✅ All 1456 tests passed

[github-actions]

🧪 Test Results — 2395216

✅ Backend (pytest) — 932 passed, 0 failed, 0 skipped (932 total)
✅ CLI (pytest) — 54 passed, 0 failed, 0 skipped (54 total)
✅ Frontend (vitest) — 405 passed, 0 failed, 0 skipped (405 total)
✅ E2E (Playwright) — 68 passed, 0 failed, 0 skipped (68 total)

Summary: ✅ All 1459 tests passed