Let the dashboard's sort dropdown span the shares card

The sort select above the admin dashboard's shares list was capped at
20rem by the admin-shares-sort wrapper. The wrapper and its rule in
app.css are gone, so the select stretches with the card's stack like
the other fields. CHANGELOG (Unreleased) notes it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `docker-compose.example.yml` mounts `sealshare_database` at `/app/database/sqlite` and sets `DB_DATABASE` to the file in it. To switch an existing install, mount the same volume there and set `DB_DATABASE: /app/database/sqlite/database.sqlite` in both services; the database is kept.
 - A share that reached its download limit is closed at once, but deleted by the hourly cleanup 24 hours after its last download instead of immediately, so downloads still running can finish. Until then its files still count towards the storage quota.
 - The download page of a share with a download limit says how many downloads are left, or how long the recipient can still download. The admin dashboard shows downloads as "2 of 3 downloads", marks shares at their limit as "Download limit reached" and no longer counts them as active.
+- The sort dropdown on the admin dashboard spans the full width of the shares card.
 
 ## [2.1.0] - 2026-09-16