GSOC-E2E: Multi-file/Multi-folder sketch management

[Geethegreat]

Issue:

Fixes #

Adds tests to verify multi-file and multi-folder sketch feature

Demo:

e2e-multifile.mp4

e2e-multifolder.1.mp4

Changes:

• Adds two E2E tests to editor.spec.ts covering the multi-file sketch feature: creating additional .js files, registering them in index.html via <script> tags, and running the resulting sketch.
• User can create a functioning sketch with multiple files: creates fileA.js at the sketch root, wires it into index.html, calls it from sketch.js, verifies it runs, then deletes fileA.js and confirms the sketch breaks accordingly (fileA is not defined).
• user can create a functioning sketch with folders: same flow, but fileA.js/fileB.js live in two separate folders (folderA, folderB) rather than side by side, to actually exercise folder-boundary resolution. After deleting folderA, verifies folderB/fileB.js is untouched, confirming folder deletion is properly scoped to just the deleted folder and its contents.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines