add(metadata): hardcover and google books as ebook providers

README.md

@@ -22,14 +22,17 @@ the same mount, otherwise moving turns into copy + delete.
 | `WORDARR_CONFIG_DIR` | `/config` | location of the SQLite database |
 | `WORDARR_AUDIBLE_REGIONS` | `de,com` | Audible marketplaces, first ranks first |
 | `WORDARR_MUSICBRAINZ_UA` | see `metadata/musicbrainz.py` | user agent MusicBrainz requires |
+| `WORDARR_HARDCOVER_TOKEN` | – | Hardcover API token, the best ebook source; without it Hardcover is skipped |
+| `WORDARR_GOOGLE_BOOKS_KEY` | – | optional, only needed when the keyless Google Books quota runs dry |
 
 ## Usage
 
 1. **Libraries** – create one per target folder with a media type, a naming
    scheme (`{Author}` `{Authors}` `{Narrator}` `{Narrators}` `{Title}` `{Year}`
    `{Series}` `{Volume}`) and optionally a language that filters the search.
-2. **Search** – look up a title (ebooks: Open Library, audiobooks: Audible plus
-   MusicBrainz, manga: AniList) and request it, or add it by hand. For a series,
+2. **Search** – look up a title (ebooks: Hardcover, Google Books and Open
+   Library, audiobooks: Audible plus MusicBrainz, manga: AniList) and request
+   it, or add it by hand. The language filter narrows ebook and audiobook hits. For a series,
    *Ganze Serie…* requests every episode at once.
 3. **Import** – scan the download folder. wordarr suggests file→request matches,
    which you confirm or correct; entries can be merged, split, or turned into