Fixes the 'cannot push until pulling first' wall on books downloaded
via OPDS. Root cause chain: the bookhoard koreader plugin only learns
the book UUID from a successful push response, but the first push had
to match by SHA-256 alone - and that match consulted only
media_items.file_sha256, missing converted formats. When the hash
missed, no UUID was returned, so pull stayed blocked (it requires the
UUID) and the book could not sync at all.
Resolution side - route all five SHA-256 match sites through the shared
BookResolver so they are format-aware:
- resolveBookToMediaItem priority 2
- SyncBookmarks book-level lookup
- per-bookmark, per-note, and per-highlight override lookups
Exposure side - return the canonical hash so clients can learn and
cache it from a pull regardless of how the book was obtained:
- KOReaderMetadata gains sha256, populated from mediaItem.FileSha256
- KOReaderLibraryBook gains sha256, populated the same way, so the
library list endpoint carries it for every book
Together with the plugin-side UUID bootstrap (bookhoard.koplugin),
push and pull now work in either order on any format.