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)

shell.nix

@@ -0,0 +1,24 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  name = "effigenix-frontend";
+
+  buildInputs = with pkgs; [
+    nodejs_22
+    nodePackages.pnpm
+
+    # Optional: useful CLI tools during development
+    jq   # JSON processing for manual API testing
+    curl # Manual HTTP requests
+  ];
+
+  shellHook = ''
+    echo "Node  $(node --version)"
+    echo "npm   $(npm --version)"
+    echo "pnpm  $(pnpm --version)"
+    echo ""
+    echo "Run 'pnpm install' to install dependencies."
+    echo "Run 'pnpm run build' to build all packages."
+    echo "Run 'pnpm run dev' to start the TUI in watch mode."
+  '';
+}