feat: implement calculator app with pseudo-auth and CI/CD

- Calculator with full keyboard support and click interaction
- Pseudo-auth via localStorage (any login accepted)
- Dark theme (AntD ConfigProvider + custom styles)
- Responsive layout from 320px
- CI/CD: service.yaml + .drone.yml for deployment to test-calculator.vigdorov.ru

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/context/AuthContext.tsx

@@ -0,0 +1,39 @@
+import { createContext, useContext, useState, useCallback, type ReactNode } from 'react';
+
+interface AuthContextType {
+  user: string | null;
+  login: (name: string) => void;
+  logout: () => void;
+}
+
+const STORAGE_KEY = 'calculator_user';
+
+const AuthContext = createContext<AuthContextType | null>(null);
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [user, setUser] = useState<string | null>(
+    () => localStorage.getItem(STORAGE_KEY),
+  );
+
+  const login = useCallback((name: string) => {
+    localStorage.setItem(STORAGE_KEY, name);
+    setUser(name);
+  }, []);
+
+  const logout = useCallback(() => {
+    localStorage.removeItem(STORAGE_KEY);
+    setUser(null);
+  }, []);
+
+  return (
+    <AuthContext.Provider value={{ user, login, logout }}>
+      {children}
+    </AuthContext.Provider>
+  );
+}
+
+export function useAuth() {
+  const ctx = useContext(AuthContext);
+  if (!ctx) throw new Error('useAuth must be used within AuthProvider');
+  return ctx;
+}