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

TODO.md

@@ -25,6 +25,13 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-14: `quak backup` no longer asks the server for changes every 3
+  seconds while it runs (issue 183). It opens its library with
+  `refreshIntervalSeconds: Infinity`, which the library now takes as no
+  background timer, so the backup refreshes only as it starts and no timed
+  refresh starts another ML data pass during the run. A test holds a backup's
+  download open while two hours pass and counts its `/collections/v2` requests.
+
 - 2026-10-14: `test/cli/backup-end-to-end.test.ts` runs `quak backup` as cron
   does (issue 186): `backupCommand` and `run`, the real `loadSession` reading a
   session saved after logging in, and every request answered by a fake of the