Move import state into ImportPage; share translation list via hook

The session-list import form, preview, and runEpisodeImport now live in
ImportPage. useAvailableTranslations fetches the translation list once per
visit for both Import and Setup. Drops the never-read importFile state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/hooks/useAvailableTranslations.js

@@ -0,0 +1,25 @@
+// The list of Bible translations offered by the HelloAO API, fetched once per
+// visit and shared by every page that needs it (Setup, Import).
+import { useEffect, useState } from 'react';
+
+let cached = null;
+let pending = null;
+
+export function useAvailableTranslations() {
+  const [translations, setTranslations] = useState(cached ?? ['BSB']);
+  useEffect(() => {
+    if (cached) return;
+    pending ??= fetch('https://bible.helloao.org/api/available_translations.json')
+      .then((res) => res.json())
+      .then((data) => {
+        if (Array.isArray(data) && data.length > 0) cached = data;
+        return cached;
+      })
+      .catch(() => null)
+      .finally(() => { pending = null; });
+    let active = true;
+    pending.then((list) => { if (active && list) setTranslations(list); });
+    return () => { active = false; };
+  }, []);
+  return translations;
+}