feat(auth): implement session store - token + user management

frontend/src/lib/session.ts

@@ -1,2 +1,34 @@
-export type SessionUser = { username: string; role: string } | null;
+const TOKEN_KEY = 'nm_token';
-export function getSessionUser(): SessionUser { return null; }
+
+export type SessionUser = {
+  id: number;
+  username: string;
+  email: string | null;
+  role: string;
+  disabled: boolean;
+  force_password_change: boolean;
+} | null;
+
+let _token: string | null = null;
+let _user: SessionUser = null;
+
+export function getToken(): string | null {
+  if (_token) return _token;
+  _token = window.localStorage.getItem(TOKEN_KEY);
+  return _token;
+}
+
+export function setToken(token: string): void {
+  _token = token;
+  window.localStorage.setItem(TOKEN_KEY, token);
+}
+
+export function clearSession(): void {
+  _token = null;
+  _user = null;
+  window.localStorage.removeItem(TOKEN_KEY);
+}
+
+export function getSessionUser(): SessionUser { return _user; }
+export function setSessionUser(user: SessionUser): void { _user = user; }
+export function isAdmin(): boolean { return _user?.role === 'admin'; }