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/(auth)/_layout.tsx

@@ -0,0 +1,5 @@
+import { Stack } from 'expo-router'
+
+export default function AuthLayout() {
+  return <Stack screenOptions={{ headerShown: false }} />
+}

memento-mobile/app/(auth)/login.tsx

@@ -0,0 +1,98 @@
+import { useState } from 'react'
+import {
+  View,
+  Text,
+  TextInput,
+  TouchableOpacity,
+  KeyboardAvoidingView,
+  Platform,
+  ActivityIndicator,
+  Alert,
+} from 'react-native'
+import { useAuthStore } from '@/lib/store'
+
+export default function LoginScreen() {
+  const [email, setEmail] = useState('')
+  const [password, setPassword] = useState('')
+  const [loading, setLoading] = useState(false)
+  const login = useAuthStore((s) => s.login)
+
+  const handleLogin = async () => {
+    if (!email.trim() || !password.trim()) return
+    setLoading(true)
+    try {
+      await login(email.trim().toLowerCase(), password)
+    } catch (e: any) {
+      Alert.alert('Connexion échouée', e.message)
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  return (
+    <KeyboardAvoidingView
+      behavior={Platform.OS === 'ios' ? 'padding' : 'height'}
+      className="flex-1 bg-paper"
+    >
+      <View className="flex-1 justify-center px-8">
+        {/* Logo */}
+        <View className="mb-12 items-center">
+          <Text className="text-4xl font-serif text-ink italic tracking-tight">Momento</Text>
+          <Text className="text-sm text-concrete mt-1">Votre espace de connaissance</Text>
+        </View>
+
+        {/* Form */}
+        <View className="space-y-3">
+          <View>
+            <Text className="text-[11px] font-semibold uppercase tracking-widest text-concrete mb-1.5">
+              Email
+            </Text>
+            <TextInput
+              value={email}
+              onChangeText={setEmail}
+              placeholder="vous@exemple.com"
+              autoCapitalize="none"
+              keyboardType="email-address"
+              autoComplete="email"
+              className="w-full border border-border rounded-xl px-4 py-3 text-ink text-[15px] bg-white"
+              placeholderTextColor="#8A8A82"
+            />
+          </View>
+
+          <View>
+            <Text className="text-[11px] font-semibold uppercase tracking-widest text-concrete mb-1.5">
+              Mot de passe
+            </Text>
+            <TextInput
+              value={password}
+              onChangeText={setPassword}
+              placeholder="••••••••"
+              secureTextEntry
+              autoComplete="password"
+              className="w-full border border-border rounded-xl px-4 py-3 text-ink text-[15px] bg-white"
+              placeholderTextColor="#8A8A82"
+              onSubmitEditing={handleLogin}
+            />
+          </View>
+
+          <TouchableOpacity
+            onPress={handleLogin}
+            disabled={loading || !email || !password}
+            className="mt-4 bg-ink rounded-xl py-3.5 items-center active:opacity-80"
+            style={{ opacity: loading || !email || !password ? 0.5 : 1 }}
+          >
+            {loading ? (
+              <ActivityIndicator color="white" size="small" />
+            ) : (
+              <Text className="text-paper font-semibold text-[15px]">Se connecter</Text>
+            )}
+          </TouchableOpacity>
+        </View>
+
+        <Text className="text-center text-[12px] text-concrete mt-8">
+          memento-note.com
+        </Text>
+      </View>
+    </KeyboardAvoidingView>
+  )
+}