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

TODO.md

@@ -26,6 +26,12 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-18: `quak files` takes the collection ID as an optional argument
+  instead of the `--collection` option, which is gone (issue 211). With no
+  argument it lists every file in the account once, collection by collection; a
+  file in several collections is listed with the first of them, which is its
+  `collectionID` in `--json`. The fresh read in `src/cli-read.ts` does this.
+
 - 2026-10-18: `quak collections` no longer waits for the files of every
   collection (issue 210). On an empty cache it opened its library with a refresh
   that fetched and decrypted the files of each collection in turn, printing