feat: add user accounts, authentication, and game history with Prisma 7

- Implement user registration and login with NextAuth v5 (email/password, JWT)
- Add authentication modal in UI with login/register tabs
- Create user profile screen showing game statistics and history
- Integrate Prisma 7 ORM with SQLite database for data persistence
- Store game results (mode, path, clicks, time) in database
- Auto-save completed games only when user is authenticated
- Separate business logic into reusable hooks (useSoloGame, useMultiGame)
- Organize UI into composable screen components (HomeScreen, SoloScreen, ProfileScreen, etc)
- Add session persistence across F5 refresh for solo and multiplayer
- Style auth modal, account button, and profile stats dashboard

lib/session.ts

@@ -0,0 +1,34 @@
+// Persistence sessionStorage pour F5 / rechargement de page
+
+const KEY = "wikirace_session";
+
+export type SessionData = {
+  screen: "solo" | "lobby" | "game";
+  // Solo
+  soloPuzzle?: { start: string; target: string };
+  soloHistory?: string[];
+  soloClicks?: number;
+  // Multi
+  multiRoomCode?: string;
+  multiPlayerId?: string;
+  playerName?: string;
+};
+
+export function saveSession(data: SessionData) {
+  try {
+    sessionStorage.setItem(KEY, JSON.stringify(data));
+  } catch { /* ignore quota */ }
+}
+
+export function loadSession(): SessionData | null {
+  try {
+    const raw = sessionStorage.getItem(KEY);
+    return raw ? (JSON.parse(raw) as SessionData) : null;
+  } catch {
+    return null;
+  }
+}
+
+export function clearSession() {
+  try { sessionStorage.removeItem(KEY); } catch { /* ignore */ }
+}