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.

internal/database/queries/queries.sql

@@ -662,7 +662,14 @@ SELECT
   mi.tags_search,
   mi.contributors_search,
   mi.narrators,
+  mi.narrators_search,
   mi.abridged,
+  mi.subtitle,
+  mi.explicit,
+  mi.authors,
+  mi.authors_search,
+  mi.publishers,
+  mi.publishers_search,
   mi.audio_metadata,
   mi.file_sha256,
   mi.opf_identifier,