css: drop dead selectors (.app-footer, #submit-btn, .form-row, .pf-restore)

The .app-footer rule was kept "for /api/health" but the health page
doesn't reference it. #submit-btn and .form-row were leftovers from
the removed upload page. .pf-restore had a class attribute in
portfolio.js but no CSS rule — dropped the class attribute too.

Also removed the @media (prefers-color-scheme: dark) block — the
dashboard JS always sets data-theme so the media query was unreachable.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/static/js/portfolio.js

@@ -220,7 +220,7 @@
       ? new Date(status.updated_at).toISOString().replace('T', ' ').slice(0, 16) + ' UTC'
       : '—';
     mount.innerHTML =
-      '<div class="pf-restore" style="padding:16px;">' +
+      '<div style="padding:16px;">' +
         '<div class="result__head">▸ Restore from cloud</div>' +
         '<div class="result__row" style="margin-bottom:12px;">' +
           'A synced portfolio is available for this account (last synced ' +