This commit introduces support for OPDS 1.2 facets, enabling advanced filtering and sorting in compatible catalogs.
To maintain a clean and uncluttered book list, facet options are presented in a dedicated context menu. When a catalog provides facets or a search link, the top-left button now triggers a menu with all available actions.
- Facet links are parsed and grouped by the `opds:facetGroup` attribute.
- The context menu includes facet groups, search, and bookmarking.
- Adds support for `opds:activeFacet` and `thr:count`.
- The parsing logic now cleanly separates feed-level links from entries, correctly handling catalogs with facets but no initial items.
- Unrelated style changes were reverted and the test suite was improved for reliability.
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