feat: App mobile Expo + API mobile dédiée

memento-mobile/ (Expo + React Native + expo-router):
- Auth: login email/password → Bearer token (expo-secure-store)
- Layout: guard auth → redirect /(auth)/login ou /(tabs)/home
- Tabs: Accueil, Carnets, Recherche, Profil
- Screens: login, home (recent notes + quick actions), notebooks list,
  note viewer (WebView HTML), search (texte), notebook detail, profile
- Design: tokens brand-accent (#A47148), ink, concrete, paper, border
- lib/config.ts: API_URL dev/prod configurable
- lib/api.ts: apiFetch avec Bearer token automatique
- lib/store.ts: Zustand auth store (login/logout/restore)

memento-note/ (API mobile dédiée):
- lib/mobile-auth.ts: createMobileToken / verifyMobileToken (HMAC-SHA256, 90j)
- POST /api/mobile/auth/login: email+password → token + user
- GET /api/mobile/auth/me: valider token, retourner profil
- GET /api/mobile/notebooks: liste carnets avec nb notes
- GET /api/mobile/notes: notes récentes (filtre par carnet optionnel)
- GET /api/mobile/notes/[id]: contenu complet d'une note
- GET /api/mobile/search: recherche fulltext titre+contenu

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

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

@@ -0,0 +1,106 @@
+import { useState } from 'react'
+import {
+  View, Text, TextInput, FlatList,
+  TouchableOpacity, ActivityIndicator,
+} from 'react-native'
+import { SafeAreaView } from 'react-native-safe-area-context'
+import { Search as SearchIcon, X } from 'lucide-react-native'
+import { useRouter } from 'expo-router'
+import { apiFetch } from '@/lib/api'
+import { ENDPOINTS } from '@/lib/config'
+
+interface SearchResult {
+  id: string
+  title: string
+  snippet: string
+  notebookName?: string
+  score?: number
+}
+
+export default function SearchScreen() {
+  const [query, setQuery] = useState('')
+  const [results, setResults] = useState<SearchResult[]>([])
+  const [loading, setLoading] = useState(false)
+  const [searched, setSearched] = useState(false)
+  const router = useRouter()
+
+  const handleSearch = async () => {
+    if (!query.trim()) return
+    setLoading(true)
+    setSearched(true)
+    try {
+      const res = await apiFetch(`${ENDPOINTS.search}?q=${encodeURIComponent(query)}`)
+      if (res.ok) {
+        const data = await res.json()
+        setResults(data.results ?? [])
+      }
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  return (
+    <SafeAreaView className="flex-1 bg-paper">
+      <View className="px-5 pt-4 pb-2">
+        <Text className="text-2xl font-serif italic text-ink mb-4">Recherche</Text>
+
+        <View className="flex-row items-center bg-white border border-border rounded-xl px-3 py-2.5 gap-2">
+          <SearchIcon size={16} color="#8A8A82" />
+          <TextInput
+            value={query}
+            onChangeText={setQuery}
+            placeholder="Chercher dans vos notes…"
+            className="flex-1 text-[15px] text-ink"
+            placeholderTextColor="#8A8A82"
+            returnKeyType="search"
+            onSubmitEditing={handleSearch}
+          />
+          {query.length > 0 && (
+            <TouchableOpacity onPress={() => { setQuery(''); setResults([]); setSearched(false) }}>
+              <X size={14} color="#8A8A82" />
+            </TouchableOpacity>
+          )}
+        </View>
+      </View>
+
+      {loading ? (
+        <View className="flex-1 items-center justify-center">
+          <ActivityIndicator color="#A47148" />
+        </View>
+      ) : (
+        <FlatList
+          data={results}
+          keyExtractor={(item) => item.id}
+          contentContainerClassName="px-5 pt-3 pb-8"
+          renderItem={({ item }) => (
+            <TouchableOpacity
+              onPress={() => router.push(`/note/${item.id}`)}
+              className="bg-white border border-border rounded-2xl p-4 mb-2.5 active:opacity-70"
+            >
+              <Text className="text-[15px] font-semibold text-ink" numberOfLines={1}>
+                {item.title || 'Sans titre'}
+              </Text>
+              {item.snippet && (
+                <Text className="text-[12px] text-concrete mt-1" numberOfLines={2}>
+                  {item.snippet}
+                </Text>
+              )}
+              {item.notebookName && (
+                <Text className="text-[11px] text-concrete/60 mt-1">{item.notebookName}</Text>
+              )}
+            </TouchableOpacity>
+          )}
+          ListEmptyComponent={
+            searched ? (
+              <Text className="text-concrete text-center mt-12">Aucun résultat pour "{query}"</Text>
+            ) : (
+              <Text className="text-concrete text-center mt-12 text-[13px]">
+                Tapez votre recherche puis appuyez sur Entrée
+              </Text>
+            )
+          }
+        />
+      )}
+    </SafeAreaView>
+  )
+}