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/config.ts

@@ -0,0 +1,18 @@
+// API base URL — change for dev/prod
+export const API_URL = __DEV__
+  ? 'http://192.168.1.190:3000'   // local network dev server
+  : 'https://memento-note.com'
+
+export const ENDPOINTS = {
+  login: `${API_URL}/api/mobile/auth/login`,
+  logout: `${API_URL}/api/mobile/auth/logout`,
+  me: `${API_URL}/api/mobile/auth/me`,
+  notebooks: `${API_URL}/api/mobile/notebooks`,
+  notes: (notebookId?: string) =>
+    notebookId
+      ? `${API_URL}/api/mobile/notes?notebookId=${notebookId}`
+      : `${API_URL}/api/mobile/notes`,
+  note: (id: string) => `${API_URL}/api/mobile/notes/${id}`,
+  search: `${API_URL}/api/mobile/search`,
+  dailyNote: `${API_URL}/api/notes/daily`,
+}