ci: add opt-in integration-test workflow for adk, langchain, n8n, pi

[mislavivanda]

Summary by cubic

Adds an opt-in GitHub Actions workflow to run live Daytona integration tests for packages/adk-plugin, packages/langchain-data-analysis, packages/n8n-nodes-daytona, and packages/pi-extension. Runs only on changed packages for same-repo PRs or via manual dispatch, protected by the integration-tests environment.

• New Features

  • New .github/workflows/integration.yml for live tests using DAYTONA_API_KEY.
  • Auto-runs on changed packages in same-repo PRs; manual workflow_dispatch lets you choose all, adk, langchain, n8n, or pi; fork PRs get a deferral notice.
  • Separate jobs per package with minimal installs; unchanged packages are skipped; runs are serialized per ref; header comments trimmed (no functional changes).

• Migration

  • Create an integration-tests environment with required reviewers and allow all branches.
  • Add secrets: DAYTONA_API_KEY (optional: DAYTONA_API_URL, DAYTONA_ORGANIZATION_ID).
  • Do not make this workflow a required status check.

^{Written for commit 7965d7c. Summary will update on new commits.}