fix: uniform 16px spacing above all settings sections

Removing the :first-child { padding-top: 0 } override lets every
section use the same padding: 16px 0, so the gap above Export matches
the gap above Import (and any future sections).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

css/app.css

@@ -631,7 +631,6 @@ select:focus { border-color: var(--accent); }
 /* ── SETTINGS MODAL ── */
 #settings-modal .modal-body { padding-top: 0; }
 .settings-section { padding: 16px 0; border-bottom: 1px solid var(--border); }
-.settings-section:first-child { padding-top: 0; }
 .settings-section:last-child { border-bottom: none; padding-bottom: 0; }
 .settings-section-title {
   font-size: 10px;