Setup CCA for extension integration tests

Enable VS Code extension integration tests for Copilot Coding
Agent (CCA).

Add setup steps to copilot-setup-steps.yml for running VS Code
Extension Host integration tests:
- Install xvfb and VS Code GUI dependencies (libasound2, libgbm1, etc.)
- Build the MCP server and bundle the extension
- Pre-download VS Code via new download:vscode script

Closes #123

Author: data-douser

extensions/vscode/package.json

@@ -163,21 +163,21 @@
   "devDependencies": {
     "@eslint/js": "^10.0.1",
     "@types/mocha": "^10.0.10",
-    "@types/node": "^25.3.5",
-    "@types/vscode": "^1.109.0",
-    "@vitest/coverage-v8": "^4.0.18",
+    "@types/node": "^25.5.0",
+    "@types/vscode": "^1.110.0",
+    "@vitest/coverage-v8": "^4.1.0",
     "@vscode/test-cli": "^0.0.12",
     "@vscode/test-electron": "^2.5.2",
     "@vscode/vsce": "^3.7.1",
-    "esbuild": "^0.27.3",
+    "esbuild": "^0.27.4",
     "eslint": "^10.0.3",
     "eslint-config-prettier": "^10.1.8",
     "eslint-plugin-prettier": "^5.5.5",
     "glob": "^13.0.6",
     "mocha": "^11.7.5",
     "prettier": "^3.8.1",
     "typescript": "^5.9.3",
-    "typescript-eslint": "^8.56.1",
-    "vitest": "^4.0.18"
+    "typescript-eslint": "^8.57.0",
+    "vitest": "^4.1.0"
   }
 }