feat(frontend): add reassurance strip and supported-formats section

Part of the Ombrora Convert redesign (Task 3/5).

frontend/src/components/ReassuranceStrip.jsx

@@ -0,0 +1,26 @@
+import { useTranslation } from 'react-i18next';
+import { Clock, LockKey, CloudArrowUp, HardDrives } from '@phosphor-icons/react';
+
+const ITEMS = [
+  { key: 'autoDelete', Icon: Clock },
+  { key: 'noAccount', Icon: LockKey },
+  { key: 'online', Icon: CloudArrowUp },
+  { key: 'maxSize', Icon: HardDrives },
+];
+
+export function ReassuranceStrip() {
+  const { t } = useTranslation();
+  return (
+    <section className="reassurance">
+      <h2>{t('reassurance.title')}</h2>
+      <ul className="reassurance-list">
+        {ITEMS.map(({ key, Icon }) => (
+          <li key={key}>
+            <Icon size={24} weight="regular" />
+            <span>{t(`reassurance.${key}`)}</span>
+          </li>
+        ))}
+      </ul>
+    </section>
+  );
+}