feat(frontend): TypeScript-Monorepo mit Terminal-UI für Effigenix ERP

Monorepo-Setup (pnpm workspaces) mit vier shared Packages und einer TUI-App:

Shared Packages:
- @effigenix/types: TypeScript-DTOs (UserDTO, RoleDTO, AuthDTO, Enums)
- @effigenix/config: API-Konfiguration und Shared Constants
- @effigenix/validation: Zod-Schemas für Username, E-Mail und Passwort
- @effigenix/api-client: axios-Client mit JWT-Handling (proaktiver + reaktiver
  Token-Refresh), AuthInterceptor, ErrorInterceptor, Resources für auth/users/roles

TUI (apps/cli, Ink 5 / React):
- Authentication: Login/Logout, Session-Restore beim Start, JWT-Refresh
- User Management: Liste, Anlage (Zod-Inline-Validation), Detailansicht,
  Passwort ändern, Sperren/Entsperren mit ConfirmDialog
- Role Management: Liste, Detailansicht, Zuweisen/Entfernen per RoleSelectList (↑↓)
- UX: SuccessDisplay (Auto-Dismiss 3 s), ConfirmDialog (J/N),
  FormInput mit Inline-Fehlern, StatusBar mit API-URL
- Layout: Fullscreen-Modus (alternate screen buffer), Header mit eingeloggtem User
- Tests: vitest + ink-testing-library (15 Tests)

frontend/packages/api-client/src/token-provider.ts

@@ -0,0 +1,17 @@
+/**
+ * Interface for token storage and retrieval.
+ * The CLI implementation stores tokens in ~/.effigenix/config.json.
+ */
+export interface TokenProvider {
+  /** Returns the current access token, or null if not authenticated */
+  getAccessToken(): Promise<string | null>;
+
+  /** Returns the current refresh token, or null if not authenticated */
+  getRefreshToken(): Promise<string | null>;
+
+  /** Persists new tokens after a successful login or refresh */
+  saveTokens(accessToken: string, refreshToken: string, expiresAt: string): Promise<void>;
+
+  /** Clears all stored tokens (called on logout or session expiry) */
+  clearTokens(): Promise<void>;
+}