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

bin/quak.ts

@@ -78,14 +78,15 @@ program
 
 program
     .command("files")
-    .description("List files in a collection")
-    .requiredOption(
-        "--collection <id>",
-        "Collection ID (from `quak collections`)",
+    .description("List the files in a collection, or every file in the account")
+    .argument(
+        "[collectionID]",
+        "Collection ID (from `quak collections`); without it, every file " +
+            "is listed once",
     )
     .option("--json", "Output as JSON array")
-    .action((opts: { collection: string; json?: boolean }) =>
-        run(filesCommand(context(), opts)),
+    .action((collectionID: string | undefined, opts: { json?: boolean }) =>
+        run(filesCommand(context(), collectionID, opts)),
     );
 
 program