Build Routes tab with paginated list and Zod-validated API responses

Routes tab (Phase 3.1):
- Paginated FlatList fetching from Journal REST API
- Route cards with name, distance (km), elevation gain, day count
- Pull-to-refresh, loading spinner, error state with retry, empty state
- Safe area insets for notch and tab bar

API client:
- Import types from @trails-cool/api instead of hand-written interfaces
- Parse list/detail responses through Zod schemas at runtime
- Add zod as mobile app dependency

i18n:
- Add mobile namespace (en + de) for routes, activities, profile, login

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mobile/package.json

@@ -33,7 +33,8 @@
     "react": "19.2.0",
     "react-native": "0.83.4",
     "react-native-safe-area-context": "~5.6.2",
-    "react-native-screens": "~4.23.0"
+    "react-native-screens": "~4.23.0",
+    "zod": "^3.25.76"
   },
   "devDependencies": {
     "@testing-library/react-native": "^13.3.3",