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/tailwind.config.js

@@ -0,0 +1,21 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: ['./app/**/*.{js,jsx,ts,tsx}', './components/**/*.{js,jsx,ts,tsx}'],
+  presets: [require('nativewind/preset')],
+  theme: {
+    extend: {
+      colors: {
+        brand: '#A47148',
+        ink: '#1A1A18',
+        paper: '#FAFAF8',
+        concrete: '#8A8A82',
+        border: '#E8E6E0',
+      },
+      fontFamily: {
+        sans: ['System'],
+        serif: ['Georgia'],
+      },
+    },
+  },
+  plugins: [],
+}