Add first-party MangaPill source and distinct volume releases

docs/library-format.md

@@ -82,6 +82,14 @@ Different source UUIDs remain distinct releases; no content equivalence is guess
 Numeric IDs and source-version folders are unchanged. Older reader releases ignore
 these new folders but retain them on disk; upgrade again to restore visibility.
 
+Whole-volume WeebCentral releases use the analogous
+`special-weebcentral-volume-<26-character-release-id>` chapter key. They live in
+the matching volume book and carry `releaseKind:"volume"`, `volume`, `sourceId`,
+and a `Volume N` label in `chapter.json`. This keeps an entire volume distinct
+from a numbered chapter in the same book. The default `skip-any` download policy
+also skips a whole-volume release if that book already contains numbered chapters;
+`add-source` allows the extra source edition explicitly.
+
 The number is normalised: leading zeros and trailing decimal zeros are dropped (`0010.50` → `10.5`), and an `x` prefix is kept. The result is the **key**:
 
 | Folder | Key |