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

src/cli-commands.ts

@@ -269,15 +269,21 @@ export const collectionsCommand = async (
     }
 };
 
+// Lists the files of the collection `collectionIDStr` names, or without it every
+// file in the account, each once (issue #211).
 export const filesCommand = async (
     ctx: CliContext,
-    opts: { collection: string; json?: boolean },
+    collectionIDStr: string | undefined,
+    opts: { json?: boolean },
 ): Promise<number> => {
     await init();
     const client = requireSession(ctx);
     if (!client) return 3;
-    const collectionID = parseID(ctx, "collection", opts.collection);
-    if (collectionID === undefined) return 1;
+    const collectionID =
+        collectionIDStr === undefined
+            ? undefined
+            : parseID(ctx, "collection", collectionIDStr);
+    if (collectionIDStr !== undefined && collectionID === undefined) return 1;
 
     const lib = await openReadLibrary(ctx, client, opts);
     try {