feat(filters+nav): author navigation end-to-end — arrays on every media response, deep-linkable bookshelf filters, clickable authors

Completes the A2c acceptance scenario: click an author on a book
detail page -> land on the bookshelf filtered to everything that
author wrote (including their share of co-authored books).

- Media detail + unscoped list resolved maps expose subtitle,
  explicit, authors, publishers (the library-scoped raw branch and
  the search endpoint already did — raw rows follow the SELECT).
- SearchMediaItemsUnified SELECT carries the new columns; the search
  endpoint serializes the row directly, so clients get them there too.
- book_detail.templ renders each author as a link to
  /bookshelf?author_filter=<name>.
- Bookshelf honors filter params in the URL on load (author_filter,
  series_filter, genre_filter, publisher_filter, tags_filter,
  narrator_filter, language_filter): pre-fills the form, applies it to
  the first grid load. Comma-joined values are multi-select via the
  server-side string_to_array split. Filtered views are shareable.

Pins widened: search rows (+7 keys), resolved keys (+4); changelog
entries in docs/contract_pins.md. Android follow-up plan written to
~/.opencode/plan/bookhoard-app-v2-compat.md.

templates/book_detail.templ

@@ -68,7 +68,13 @@ templ BookDetail(user User, book handlers.MediaDetail, errorMessage string, tomb
 							}
 							if len(book.Authors) > 0 {
 								<h2 class="text-lg md:text-xl mb-5" style="color: var(--text-secondary)">
-									by { strings.Join(book.Authors, ", ") }
+									by
+									for i, authorName := range book.Authors {
+										if i > 0 {
+											<span>, </span>
+										}
+										<a href={ "/bookshelf?author_filter=" + url.QueryEscape(authorName) } class="hover:underline" style="color: var(--text-secondary);">{ authorName }</a>
+									}
 								</h2>
 							} else if book.Author.Valid && book.Author.String != "" {
 								<h2 class="text-lg md:text-xl mb-5" style="color: var(--text-secondary)">