feat: add author pages with clickable author links

[tijs]

Summary

• Add /authors/:author route to browse all books by a specific author
• Make author names clickable links on book detail pages
• Each author in a multi-author book is independently clickable
• Support pagination (100 books per page) and sorting (popularity/reviews)
• Extract author matching utilities with test coverage

Implementation Details

• New file: src/pages/authorBooks.tsx - Author books listing page (modeled after genre pages)
• New file: src/utils/authorMatching.ts - Utilities for tab-separated author matching
• Modified: src/routes.tsx - Added /authors/:author route handler
• Modified: src/pages/bookInfo.tsx - Made author names clickable

Screenshots

N/A - text-based changes

Test plan

• All existing tests pass (44 tests)
• New tests for author matching utilities (18 tests)
• Navigate to a book detail page → author names should be styled as links
• Click an author → should navigate to /authors/Author%20Name
• Author page shows all books by that author with pagination
• Test with authors having special characters (periods, apostrophes)
• For co-authored books, verify each author is a separate link
• Click different co-authors → same book appears on both pages

Closes #4