mobile: fix Search import manquant + assets icon/splash

- home.tsx: remettre Search dans les imports lucide (utilisé ligne 70)
- assets/: créer icon.png, splash.png, adaptive-icon.png (évite warning Metro)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

memento-mobile/app/(tabs)/home.tsx

@@ -5,7 +5,7 @@ import {
 } from 'react-native'
 import { SafeAreaView } from 'react-native-safe-area-context'
 import { useRouter } from 'expo-router'
-import { CalendarDays, PenLine, GraduationCap, Clock, ChevronRight } from 'lucide-react-native'
+import { CalendarDays, PenLine, GraduationCap, Clock, ChevronRight, Search } from 'lucide-react-native'
 import { apiFetch } from '@/lib/api'
 import { ENDPOINTS } from '@/lib/config'
 import { useAuthStore } from '@/lib/store'