Rename Brain to Upload material and Instruction to Brain and AI

Upload material (/upload) drops the metric cards for a larger upload box
above the material list; Brain and AI moves to /brain. Old paths redirect.

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

src/pages/Schedule.tsx

@@ -24,7 +24,7 @@ export function SchedulePage() {
   return (
     <>
       <PageHead title={t('sch.title')} description={t('sch.description')}
-        actions={<Link className="btn primary" to="/instruction"><Icon name="plus" />{t('sch.newInstruction')}</Link>} />
+        actions={<Link className="btn primary" to="/brain"><Icon name="plus" />{t('sch.newInstruction')}</Link>} />
       <div className="card">
         <div className="card-head"><h3>{t('sch.cardTitle')}</h3><Icon name="calendar" /></div>
         {schedules.isPending && <SkeletonRows label={t('sch.loading')} />}