quak files takes the collection ID as an optional argument (closes #211)

Mandatory arguments are positional, so `quak files` takes the collection
ID as an optional argument and the `--collection` option is removed.
With a collection ID it lists that collection's files. Without one it
lists every file in the account, collection by collection, each file
once: the library keeps a record of a file for each collection that
holds it, and only the first collection's record is listed, so that
collection is its `collectionID` in `--json`. The `--help` text, the
README and `TODO.md` say so.

Model: opus-5-5

test/cli/backup-undecryptable.test.ts

@@ -548,7 +548,7 @@ describe("the read commands with records quak cannot decrypt", () => {
         expect(await collectionsCommand(context(ente), {})).toBe(0);
         expect(stdout.text).toBe("1\talbum\tTrip\n");
 
-        expect(await filesCommand(context(ente), { collection: "1" })).toBe(0);
+        expect(await filesCommand(context(ente), "1", {})).toBe(0);
         expect(stdout.text).toBe("10\timage\tphoto-10.jpg\n");
     });
 });