Typecheck scripts, fix convertFourslash

[jakebailey]

We never checked this in CI, so we managed to commit errors.

Add CI checks, and then take my fix from #3304.

[Copilot]

Pull request overview

This PR adds CI coverage to TypeScript-based repo scripts by introducing a dedicated type-check task, and fixes a TypeScript type-check failure in the fourslash conversion script (ported from #3304) so it can be reliably checked in CI.

Changes:

• Fix convertFourslash.mts to throw (instead of returning undefined) on unsupported/invalid organizeImportsTypeOrder preference values, resolving a TS type-check issue.
• Add a hereby task (check:scripts) that runs tsc -p across the repo’s script tsconfigs.
• Update CI to run npm ci and execute npx hereby check:scripts in the misc job.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/fourslash/_scripts/convertFourslash.mts	Makes preference parsing type-safe and consistent by throwing on invalid organizeImportsTypeOrder inputs.
Herebyfile.mjs	Adds a check:scripts task to type-check script tsconfigs with tsc.
.github/workflows/ci.yml	Ensures scripts are type-checked in CI by installing Node deps and running check:scripts.