feat: add session export with full and compressed modes (#507)

Add export functionality that allows users to download session data
as JSON or plain text, with optional LLM-based context compression
for long conversations. Includes UI controls in chat panel, session
list, and history view, plus i18n strings for all 8 locales.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

packages/client/src/i18n/locales/fr.ts

@@ -151,6 +151,12 @@ export default {
     monitorRoleUser: 'Utilisateur',
     monitorRoleAssistant: 'Assistant',
     copySessionId: "Copier l'ID de session",
+    export: 'Exporter',
+    exportFull: 'Export complet (JSON)',
+    exportCompressed: 'Export compressé (TXT)',
+    exportCompressing: 'Compression du contexte, veuillez patienter...',
+    exportSuccess: 'Session exportée',
+    exportFailed: "Échec de l'export",
     renamed: 'Renomme',
     renameFailed: 'Echec du renommage',
     renameSession: 'Renommer la session',