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/lib/api.ts

@@ -0,0 +1,27 @@
+import * as SecureStore from 'expo-secure-store'
+
+const TOKEN_KEY = 'memento_token'
+
+export async function getToken(): Promise<string | null> {
+  return SecureStore.getItemAsync(TOKEN_KEY)
+}
+
+export async function setToken(token: string): Promise<void> {
+  await SecureStore.setItemAsync(TOKEN_KEY, token)
+}
+
+export async function clearToken(): Promise<void> {
+  await SecureStore.deleteItemAsync(TOKEN_KEY)
+}
+
+export async function apiFetch(url: string, options: RequestInit = {}): Promise<Response> {
+  const token = await getToken()
+  return fetch(url, {
+    ...options,
+    headers: {
+      'Content-Type': 'application/json',
+      ...(token ? { Authorization: `Bearer ${token}` } : {}),
+      ...options.headers,
+    },
+  })
+}