One album or file quak cannot decrypt no longer stops a refresh or a backup (closes #181)

collectionsSince and filesSince put a row that does not decrypt or parse in
an undecryptable list with the reason instead of throwing. The refresh
leaves it out, an album with its files, and the store keeps the list in
metadata.json until the server sends a copy that decrypts or deletes it,
since the next refresh asks only for changes. lib.backup() records each
such file in failures.json as "could not be decrypted: <reason>", unless a
copy in another album decrypted, logs one line per such album and lists
their IDs in undecryptableAlbums; quak backup exits 1 while any remain.
Tests use a stand-in Ente server with real encryption.

Model: opus-5-5

test/cli/backup.test.ts

@@ -1482,6 +1482,7 @@ describe("backup album folders", () => {
         listCollections: () => albums.map((a) => a.collection),
         listFiles: (id) =>
             albums.find((a) => a.collection.id === id)?.files ?? [],
+        undecryptable: () => [],
         original: async (fileID) => {
             const path = join(root, `source-${fileID}`);
             writeFileSync(path, `original ${fileID}`);