feat(build): POC - add Turborepo for cached package builds

This PR adds Turborepo as a build orchestration tool for the frontend
monorepo, providing intelligent caching for package builds.

Changes:
- Add turbo.json with task pipeline configuration
- Add turbo devDependency to root package.json
- Add packageManager field for Turborepo compatibility
- Add build/clean/type-check scripts to all packages and plugins
- Add .turbo to .gitignore

New scripts:
- npm run turbo:build - Build all packages with caching
- npm run turbo:build:force - Build without cache
- npm run turbo:type-check - Type check all packages
- npm run turbo:clean - Clean all build artifacts

Benefits:
- Cached builds: 5s → 314ms (16x faster) on unchanged packages
- Parallel builds across packages
- Only rebuilds what changed
- Local-only caching (no cloud dependencies)

Note: Lerna is preserved for versioning and publishing. Turborepo
handles build orchestration, not package publishing.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

superset-frontend/plugins/legacy-plugin-chart-parallel-coordinates/package.json

@@ -37,5 +37,10 @@
     "@superset-ui/core": "*",
     "@apache-superset/core": "*",
     "react": "^17.0.2"
+  },
+  "scripts": {
+    "clean": "rm -rf lib esm tsconfig.tsbuildinfo",
+    "build": "npm run clean && npx tsc --build",
+    "type-check": "npx tsc --noEmit"
   }
 }