feat: parse and display all available EPUB metadata fields

Add parsing for dc:publisher, dc:date, dc:subject, dc:rights,
dc:contributor, dc:identifier (prefers ISBN scheme), and
calibre:rating. All new fields serialized in BookMetadataCache
(version bumped to 7) and displayed in BookInfoActivity with
rating shown as N/5 scale.

Made-with: Cursor

lib/I18n/I18nKeys.h

@@ -452,6 +452,13 @@ enum class StrId : uint16_t {
   STR_SERIES,
   STR_FILE_SIZE,
   STR_DESCRIPTION,
+  STR_PUBLISHER,
+  STR_DATE,
+  STR_SUBJECTS,
+  STR_RATING,
+  STR_ISBN,
+  STR_RIGHTS,
+  STR_CONTRIBUTOR,
   STR_MANAGE,
   STR_INFO,
   STR_ARCHIVE_BOOK,