Queue up to 1024 commands, so Download latest 100 does not hang (#154)

The worker's queue held 64 commands, and a web request that queues work waits inside itself for a
free place. Download latest lets you ask for up to 100 and sends one command a file, so past 64
the request waited for the worker to finish whole downloads, one after another, an hour for 100;
Cloudflare gave up on it after 100 s and the page said it failed, though most were queued. Until
it finished, adding a feed, Refresh, Download and socket commands all waited for a place too. A
command is a few bytes; the queue now has room for any one request's.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Downloading the latest 65 to 100 items of a feed queues them at once, instead of hanging until most had downloaded and holding up adding feeds and Refresh meanwhile.
 - Changes to the feed list made at the same moment, such as two people adding feeds, or a feed added while the server settings change, no longer undo one another.
 - A download that stops partway is given up after two minutes without data, instead of holding up every scan and download until a restart.
 - On a phone, the closed feed list no longer shades the left edge of the page with its shadow.