Fix dashboard black screen, add login gate, and expand README.

Pin React Three Fiber to React 18, remove PWA caching, add SessionGate and error boundaries, and document movie fusion, auth, outputs, and troubleshooting.

server/web/src/pages/DashboardPage.tsx

@@ -10,6 +10,7 @@ import { FleetPipelineStatus, ActivityPulse } from '../components/Visual/VisualC
 import { AlertBanner, PoolStatusPanel, AIActivityPanel, EarningsEstimator } from '../components/Fleet/FleetPanels';
 import AgentRemoteActions from '../components/Fleet/AgentRemoteActions';
 import FleetToolbar from '../components/Fleet/FleetToolbar';
+import ErrorBoundary from '../components/ErrorBoundary';
 import FleetTopologyMap from '../components/Visual/3D/FleetTopologyMap';
 import MatrixStreamOverlay from '../components/Visual/MatrixStreamOverlay';
 import {
@@ -246,7 +247,15 @@ export default function DashboardPage() {
       </NeonCard>
 
       <section className="section">
-        <FleetTopologyMap agents={agents} />
+        <ErrorBoundary
+          fallback={
+            <div className="card">
+              <p className="form-hint">3D fleet map unavailable on this GPU — rest of the deck still works.</p>
+            </div>
+          }
+        >
+          <FleetTopologyMap agents={agents} />
+        </ErrorBoundary>
       </section>
 
       <section className="section">