Give the folder triangle a wider gutter

The feed list's left padding grows from 8 to 16 px and the triangle's
button from 16 to 24 px wide, so it is no longer cramped against the
folder's art. Everything in the list shifts together, so feeds still line
up with the places above.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TAC7sLVqfKmY6rsTLXzNgk

CHANGELOG.md

@@ -10,6 +10,10 @@ The long form, with what was wrong before and how it was found, is in
 
 ## [Unreleased]
 
+### Changed
+
+- The triangle that opens an OPML or Patreon folder has more room, and a wider target to click.
+
 ## [0.5.0] - 2026-09-12
 
 ### Added