fix(frontend): i18n reactive badges + aria-labels + ExportEngagementButton + noMatch (review polish)

- ExportEngagementButton: full i18n (export.btn, export.btnLoading, export.aria)
- Layout: aria-label nav.brandHome on brand link, nav.themeAria on theme button
- SimulationList: aria-label simulation.list.rowActions on chevron button
- C2TasksPanel: aria-label c2.tasks.col.expand on expand column header
- ImportC2HistoryModal: aria-label common.select on select column header
- MitreMatrixModal: common.collapse/expand interpolated aria-label + mitre.matrix.noMatch
- fr.json: new keys common.expand/collapse/select, nav.brandHome/themeAria, export.*, simulation.list.rowActions, mitre.matrix.noMatch, c2.tasks.col.expand

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

frontend/src/components/ImportC2HistoryModal.tsx

@@ -140,7 +140,7 @@ export function ImportC2HistoryModal({
                   <table className="w-full text-[14px]">
                     <thead>
                       <tr className="bg-cloud border-b border-hairline">
-                        <th className="px-md py-sm w-8" aria-label="Select" />
+                        <th className="px-md py-sm w-8" aria-label={t('common.select')} />
                         <th className="px-md py-sm text-left font-medium text-ink">#</th>
                         <th className="px-md py-sm text-left font-medium text-ink">{t('c2.tasks.col.command')}</th>
                         <th className="px-md py-sm text-left font-medium text-ink">{t('c2.tasks.col.status')}</th>