feat: Add data export/import functionality (#22)

* feat: add data export/import functionality

- Add /export and /import API endpoints with schema-independent JSON format
- Export includes: medications, dose history, settings, share links
- Uses _exportId references for medications, remapped on import
- Images exported as base64 data URLs
- Optional sensitive data inclusion (shoutrrr URLs, etc.)
- Import replaces all existing data with confirmation warning
- Add comprehensive test coverage
- Add English and German translations
- Add frontend UI in Settings page with export/import controls

* fix: correct JSX structure and TypeScript types

- Fix modal placement outside ternary expression in Settings
- Add type assertion for request.body in import route test

* docs: translate copilot-instructions to English

- Add explicit rule that English is the primary language
- Translate all German sections to English
- User may communicate in German, but all project artifacts must be English

frontend/src/i18n/de.json

@@ -348,5 +348,27 @@
       "contact": "Bitte kontaktiere {{username}} um einen neuen Link anzufordern.",
       "expiredOn": "Abgelaufen am: {{date}}"
     }
+  },
+  "exportImport": {
+    "title": "Daten Export / Import",
+    "description": "Exportiere deine Daten zur Sicherung oder Übertragung auf ein anderes Gerät. Import ersetzt ALLE deine bestehenden Daten.",
+    "export": "Daten exportieren",
+    "exporting": "Exportiere...",
+    "import": "Daten importieren",
+    "importing": "Importiere...",
+    "selectFile": "Datei auswählen",
+    "includeSensitive": "Sensible Daten einschließen",
+    "sensitiveWarning": "Warnung: Dies fügt Benachrichtigungs-URLs (können Passwörter enthalten) im Klartext in die Exportdatei ein.",
+    "confirmImport": "Alle Daten ersetzen?",
+    "confirmImportMessage": "Dies löscht dauerhaft alle deine aktuellen Medikamente, Einnahmehistorie, Einstellungen und Teilen-Links und ersetzt sie durch die importierten Daten.",
+    "confirmImportWarning": "Diese Aktion kann nicht rückgängig gemacht werden!",
+    "confirmButton": "Ja, alles ersetzen",
+    "cancelButton": "Abbrechen",
+    "exportSuccess": "Daten erfolgreich exportiert",
+    "importSuccess": "Daten erfolgreich importiert",
+    "importSuccessDetails": "Importiert: {{medications}} Medikamente, {{doses}} Dosen, {{shares}} Teilen-Links",
+    "importError": "Daten konnten nicht importiert werden",
+    "invalidFile": "Ungültiges Dateiformat. Bitte wähle eine gültige MedAssist-Exportdatei.",
+    "downloadFilename": "medassist-export"
   }
 }

frontend/src/i18n/en.json

@@ -350,5 +350,27 @@
       "contact": "Please contact {{username}} to request a new link.",
       "expiredOn": "Expired on: {{date}}"
     }
+  },
+  "exportImport": {
+    "title": "Data Export / Import",
+    "description": "Export your data for backup or transfer to another device. Import will replace ALL your existing data.",
+    "export": "Export Data",
+    "exporting": "Exporting...",
+    "import": "Import Data",
+    "importing": "Importing...",
+    "selectFile": "Select File",
+    "includeSensitive": "Include sensitive data",
+    "sensitiveWarning": "Warning: This will include notification URLs (may contain passwords) in plain text in the export file.",
+    "confirmImport": "Replace All Data?",
+    "confirmImportMessage": "This will permanently delete all your current medications, dose history, settings, and share links, then replace them with the imported data.",
+    "confirmImportWarning": "This action cannot be undone!",
+    "confirmButton": "Yes, Replace All",
+    "cancelButton": "Cancel",
+    "exportSuccess": "Data exported successfully",
+    "importSuccess": "Data imported successfully",
+    "importSuccessDetails": "Imported: {{medications}} medications, {{doses}} doses, {{shares}} share links",
+    "importError": "Failed to import data",
+    "invalidFile": "Invalid file format. Please select a valid MedAssist export file.",
+    "downloadFilename": "medassist-export"
   }
 }