quak backup no longer refreshes its library on a timer (closes #183)

The backup opened its library with the default 3-second refresh interval,
so for its whole run it asked the server for changes every few seconds,
and each refresh started another ML data pass. It now opens it with
refreshIntervalSeconds: Infinity. The library takes Infinity as no
background timer, since setTimeout would turn it into 1 ms. A refresh
interval of 3600, as the read commands use, would still refresh once an
hour in a backup that runs for hours.

Model: opus-5-5

README.md

@@ -781,7 +781,8 @@ subsequent runs, existing originals are skipped. If a download fails, the error
 is logged and the backup continues with the next file. The exit code is non-zero
 if any files failed. `quak backup` opens its library with the thumbnail and
 originals precache off, so the only file content it fetches is the originals the
-backup stores.
+backup stores. It also opens it with no background timer, so it asks the server
+for changes only as it starts, not again while it downloads.
 
 With `--verify`, or `lib.backup({ verify: true })`, a run also hashes each
 original already at its save path the way a download is checked (see "On-disk
@@ -861,7 +862,7 @@ background, so an unreachable server does not block opening.
 | `client`                 | required                                           | the account client (a `Client`, or any `LibraryClient`)              |
 | `cacheDirectory`         | `quak/<userID>` under the per-user cache directory | where `metadata.json` and the content cache live                     |
 | `downloadDirectory`      | `photos` in the working directory                  | root of the save paths; an original stored there counts as cached    |
-| `refreshIntervalSeconds` | `3`                                                | background refresh cadence                                           |
+| `refreshIntervalSeconds` | `3`                                                | background refresh cadence; `Infinity` for no background timer       |
 | `precacheThumbnails`     | `true`                                             | prefetch every thumbnail, newest first                               |
 | `precacheOriginals`      | `true`                                             | prefetch the favorites album and the latest-window originals         |
 | `precacheOriginalsDays`  | `7`                                                | length in days of that latest window                                 |