Invalidate stale YAML validation after edits

[jmtdev0]

Summary

• Invalidate pending YAML validations when the editor content or input mode changes.
• Clear stale parsing, validation, and error state immediately after a relevant edit.
• Ignore debounced validation results that belong to an older editor version.
• Add regression coverage for rapid edits and mode changes.

Fixes #5023

Validation

• YAML import tests: 12 passing
• Prettier
• Focused ESLint
• git diff --check

The full frontend validation was not run because the repository environment is missing the phoenix_live_view/constants dependency and contains unrelated baseline TypeScript errors.

AI Disclaimer

This pull request was primarily developed with assistance from OpenAI Codex, an AI coding agent. For this PR, Codex analyzed issue #5023, inspected the relevant OpenFn Lightning code, implemented the fix, added the regression tests, and ran the reported validation commands under the supervision of jmtdev0.

Human involvement in this PR was very low.

If you do not agree with the use of AI assistance or with the level of human involvement in this PR, please feel free to disregard it, close it, or request changes. I will fully respect that decision.

[jmtdev0]

The failed \security-review\ check appears to be a workflow-permission issue rather than a problem with this PR.

The workflow runs with the \jmtdev0\ actor having read-only access to the upstream repository, so the Claude review action cannot publish its result. The follow-up attempt to create the review comment is rejected by GitHub with \403 Resource not accessible by integration.

The CircleCI compile, lint, Dialyzer, Elixir, and JavaScript checks are passing.