Add library filter, sync, and export enhancements

[kvmgithub]

Context

This PR implements the feature requests from #23 except the additional
provider integrations (Libro.fm, Downpour, Chirp), which are a separate
effort. Along the way it fixes the two bugs behind the filter symptoms
described in the issue: selecting a series after clearing filters showed
zero results, and the genre category was always empty.

Fixes #23

What changed

Filter fixes

• Series filter returned 0 results: the list query's series clause
  referenced a CTE that was never joined in that query, so any series
  selection made the whole query fail. The series/category/account
  clauses are now built by one shared helper used by both the list and
  count queries, and series matching uses an EXISTS over all of a book's
  series instead of only the first one.
• Genre was never populated: library sync parsed category_ladders
  from the API but never persisted them. Sync now stores each ladder as a
  JSON array of category names in CategoryLadders and links it via
  BookCategories; the genre list is read back with json_each. Genres
  appear after the next library sync.

Filter UI

• Accounts, genres, and series are multi-select; a book matching any
  selected value is shown.
• Genre moved above series.
• Sections with more than 10 options collapse behind a "Show all (N)"
  row; selected options stay visible while collapsed.
• New Type section (All / Audiobooks / Podcasts).

Multi-account sync

The account screen gains "Sync All Accounts" (shown when more than one
account exists), which syncs every account sequentially with one summary
at the end. Token refresh per account is preserved.

Book details

Tapping a library title opens a detail card with authors, narrators,
series, duration, release date, owning account, and the summary. Long
summaries collapse to 8 lines with Show more/less (shown only when the
text actually exceeds that). Podcast parents open the same card with a
"View Episodes" button, so the episode list is one tap further.

Two data fixes back this up:

• Sync now prefers publisher_summary (full text) over
  merchandising_summary (a teaser truncated with an ellipsis), and
  update_book now updates the stored description at all — previously
  descriptions were written once at insert and never refreshed.
• Descriptions render their original <p>/<br> structure as paragraph
  breaks instead of being flattened to one line.

Account badges

When more than one account exists, library cards show a badge with the
owning account's name next to the existing LibriVox badge.

Database export/import

Settings > Database gains Export (a consistent single-file snapshot via
VACUUM INTO, saved through the system directory picker) and Import
(SQLite-header-validated file replaces the current database after a
confirmation).

Goodreads/StoryGraph export

The library export offers a "Goodreads" format: a CSV in Goodreads import
layout (Title, Author, Binding=Audiobook, Year Published, Date Added,
Owned Copies), which StoryGraph's Goodreads importer also accepts.
Audiobooks carry no ISBN, so both services match by title/author.

User-visible behavior

1. Selecting a series shows its books (previously 0 results).
2. Genre filter has options after the next sync.
3. Multiple accounts/genres/series can be selected at once.
4. Long filter lists collapse; Type filter separates podcasts from books.
5. "Sync All Accounts" syncs every account in one run.
6. Tapping a title shows its summary card; podcast parents show it too.
7. Cards show the owning account when several accounts exist.
8. The database can be exported and re-imported from Settings.
9. Library export can produce a Goodreads/StoryGraph-compatible CSV.

Review focus

• The shared WHERE builder in queries.rs and the new
  test_list_books_with_filters_by_series_and_category covering the
  series bug, multi-select, and the json_each genre list.
• Category ladder persistence in library.rs (link_categories).
• The multi-select plumbing through the Kotlin extras JSON into
  jni_bridge.rs (legacy single-value fields still accepted).
• VACUUM INTO export and the import's header check in
  SettingsScreen.tsx.

Validation

• npm run typecheck
• cargo test -p rust-core (lib + integration suites, all green)
• Android debug build installed; verified manually on device: sync, genre
  filter populated, series selection returns hits, multi-select, detail
  card with Show more/less, podcast parent card + episodes, type filter,
  database export/import, Goodreads CSV import layout