Line up the feed sidebar

Every row reserves the chevron slot, so artwork and titles share one
column instead of stepping left when a feed has no children. Children
keep a single icon size and read as nested from the indent alone. Labels
stack on one line-height, and the unread count has a min-width so a
three-digit feed doesn't shove its own title.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AdXho5tTkjFLeUXKbEjKBh

tests/ui/app.spec.js

@@ -174,7 +174,8 @@ test('an OPML subscription is a collapsible folder', async ({ page }) => {
       body: JSON.stringify({ feed: 'test-subscriptions', force: true }),
     }));
 
-  const chev = page.locator('.feed .chev');
+  // Every row reserves the chevron slot for alignment; only a folder's is clickable.
+  const chev = page.locator('.feed.group .chev');
   await expect(chev).toBeVisible({ timeout: 20_000 });
 
   // Closed by default: the child is not listed until the folder is opened.