feat(book-requests): link releases to their source page and hold imports for review

Torznab and Newznab read the feed's details page, plugins may send infoUrl, and the
search drops any link that could carry a credential. A grab can ask to be held for
review whatever its score, and the held review shows the file's own edition facts,
its cover and the release page. Torznab guids are now digested like Newznab's.

Refs #1438

packages/plugin-api/src/index.ts

@@ -99,6 +99,12 @@ export interface PluginReleaseCandidate {
   downloadUrl?: string;
   magnet?: string;
   infoHash?: string;
+  /**
+   * The release's page on the source, for an approver to read before sending it. An http(s) URL
+   * that needs no credential: the host drops one carrying the indexer's credential or a key-like
+   * query parameter rather than showing it. Ignored by hosts older than the field.
+   */
+  infoUrl?: string;
   sizeBytes: number | null;
   /**
    * Null means the source reported no swarm counts, which must not be read as zero: the