Add CloudXR VR streaming support for PICO 4 Ultra (Early Access)

Replaces manual H264/TCP stereo streaming with NVIDIA CloudXR for
higher-quality stereoscopic rendering and lower latency.

Changes:
- teleop_xr_agent.py: add --cloudxr flag (enables Isaac Sim XR mode,
  disables manual StreamingManager)
- deps/cloudxr/: NVIDIA CloudXR.js SDK (Early Access) with Isaac Lab
  teleop React web client
- deps/cloudxr/Dockerfile.wss.proxy: HAProxy WSS proxy for PICO 4 Ultra
  HTTPS mode (routes wss://48322 → ws://49100)
- deps/cloudxr/isaac/webpack.dev.js: disable file watching to avoid
  EMFILE errors with large node_modules
- deps/cloudxr/INSTALL.md: full setup guide

Usage:
  # Start CloudXR Runtime + Isaac Lab
  cd ~/IsaacLab && ./docker/container.py start \
      --files docker-compose.cloudxr-runtime.patch.yaml \
      --env-file .env.cloudxr-runtime

  # Run teleop with CloudXR
  ~/IsaacLab/isaaclab.sh -p teleop_xr_agent.py \
      --task Isaac-MindRobot-2i-DualArm-IK-Abs-v0 --cloudxr

  # Serve web client
  cd deps/cloudxr/isaac && npm run dev-server:https

deps/cloudxr/react/webpack-plugins/DownloadAssetsPlugin.js

@@ -0,0 +1,109 @@
+const fs = require('fs');
+const path = require('path');
+const https = require('https');
+
+class DownloadAssetsPlugin {
+  constructor(assets) {
+    this.assets = assets;
+    this.hasRun = false;
+    this.createdDirs = new Set();
+  }
+
+  safeUnlink(filePath) {
+    try {
+      fs.unlinkSync(filePath);
+    } catch (err) {
+      // Ignore cleanup errors
+    }
+  }
+
+  apply(compiler) {
+    compiler.hooks.beforeCompile.tapAsync('DownloadAssetsPlugin', (params, callback) => {
+      // Only run once per webpack process
+      if (this.hasRun) {
+        callback();
+        return;
+      }
+
+      console.log('📦 Checking and downloading required assets...');
+
+      const downloadPromises = this.assets.map(asset => this.downloadFile(asset));
+
+      Promise.allSettled(downloadPromises)
+        .then((results) => {
+          const failed = results.filter(r => r.status === 'rejected');
+          if (failed.length > 0) {
+            console.warn(`⚠️  ${failed.length} asset(s) failed to download, continuing anyway...`);
+          }
+          console.log('✅ Asset check complete!');
+          this.hasRun = true;
+          callback();
+        });
+    });
+  }
+
+  downloadFile({ url, output }) {
+    return new Promise((resolve, reject) => {
+      // Ensure directory exists (only once per unique path)
+      if (!this.createdDirs.has(output)) {
+        fs.mkdirSync(output, { recursive: true });
+        this.createdDirs.add(output);
+      }
+
+      const filename = path.basename(url);
+      const filePath = path.join(output, filename);
+
+      // Skip if file already exists
+      if (fs.existsSync(filePath)) {
+        resolve();
+        return;
+      }
+
+      console.log(`  Downloading ${filename}...`);
+
+      const file = fs.createWriteStream(filePath);
+
+      const downloadFromUrl = (downloadUrl) => {
+        https.get(downloadUrl, (response) => {
+          // Handle redirects
+          if (response.statusCode === 302 || response.statusCode === 301) {
+            file.close();
+            this.safeUnlink(filePath);
+            downloadFromUrl(response.headers.location);
+            return;
+          }
+
+          if (response.statusCode !== 200) {
+            file.close();
+            this.safeUnlink(filePath);
+            reject(new Error(`Failed to download ${filename}: HTTP ${response.statusCode}`));
+            return;
+          }
+
+          response.pipe(file);
+
+          file.on('finish', () => {
+            file.close();
+            console.log(`  ✓ Downloaded ${filename}`);
+            resolve();
+          });
+
+          file.on('error', (err) => {
+            this.safeUnlink(filePath);
+            reject(err);
+          });
+        }).on('error', (err) => {
+          if (fs.existsSync(filePath)) {
+            this.safeUnlink(filePath);
+          }
+          reject(err);
+        });
+      };
+
+      downloadFromUrl(url);
+    });
+  }
+}
+
+module.exports = DownloadAssetsPlugin;
+