feat(03-05): wire App.tsx step router and make App.test GREEN

- App.tsx: WizardShell routes to BackendSelectionStep/RemoteConfigStep/DeploymentStep
- App.tsx: StepIndicator renders above every step as persistent breadcrumb
- App.tsx: RemoteConfigStep keyed on backendType to force remount on backend change
- App.test.tsx: all 3 WIZD-02 tests GREEN (step 0, 1, 2 routing verified)
- Full suite: 87 tests GREEN across 11 test files

src/App.tsx

@@ -1,12 +1,45 @@
 // src/App.tsx
+// Step router — renders the correct step component based on currentStep.
+// StepIndicator renders above each step as persistent breadcrumb navigation.
+
+import { useWizard } from './store/context';
 import { WizardProvider } from './store/context';
+import { StepIndicator } from './components/wizard/StepIndicator';
+import { BackendSelectionStep } from './components/wizard/BackendSelectionStep';
+import { RemoteConfigStep } from './components/wizard/RemoteConfigStep';
+import { DeploymentStep } from './components/wizard/DeploymentStep';
+
+function WizardShell() {
+  const { state } = useWizard();
+
+  const steps = [
+    <BackendSelectionStep key="backend" />,
+    // Key on backendType to force remount when backend changes — prevents stale form values
+    <RemoteConfigStep key={state.remote.backendType ?? 'none'} />,
+    <DeploymentStep key="deployment" />,
+  ];
+
+  // Guard: clamp to valid range (phase 4 will add step 3 for review/download)
+  const stepIndex = Math.min(state.currentStep, steps.length - 1);
+  const CurrentStep = steps[stepIndex];
+
+  return (
+    <div className="min-h-screen bg-gray-50 flex flex-col items-center py-12 px-4">
+      <div className="w-full max-w-2xl">
+        <h1 className="text-3xl font-bold text-gray-900 mb-8 text-center">Ready2Blob</h1>
+        <StepIndicator />
+        <div className="mt-8">
+          {CurrentStep}
+        </div>
+      </div>
+    </div>
+  );
+}
 
 export default function App() {
   return (
     <WizardProvider>
-      <div className="p-4">
-        <h1 className="text-2xl font-bold">Ready2Blob</h1>
-      </div>
+      <WizardShell />
     </WizardProvider>
   );
 }