Remove Excalidraw-based Sketch Lab

[molly-moen]

This PR removes the excalidraw-based Sketch Lab from the repo and gets rid of the experiment flag that allowed you to load any sketch lab level in excalidraw. We have fully moved to React Flow now.

I kept the excalidraw migrator in case there are any lingering projects or levels. This means we still need the @excalidraw import in the repo, as we rely on excalidraw's types. I added a comment to the migration file that if we ever decide to cut this off, we can remove the import.

Links

• Jira: 1829

Testing story

Tested locally that sketch lab still loads as expected.

[Copilot]

Pull request overview

Removes the legacy Excalidraw-based implementation of Sketch Lab and associated experiment gating, leaving React Flow as the sole Sketch Lab implementation while preserving Excalidraw-to-React Flow migration support.

Changes:

• Removed the EXCALIDRAW experiment flag and all Excalidraw Sketch Lab view/tour/utils/styles.
• Updated Sketch Lab to always render the React Flow implementation and simplified product-tour availability accordingly.
• Added a React Flow-local uploadBase64ToUrl helper and re-wired Excalidraw conversion uploads to use it.

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
apps/test/unit/lab2/productTours/productToursPerLabTest.ts	Updates product tour tests to reflect removal of Excalidraw tour and experiment gating.
apps/src/util/experiments.js	Removes experiments.EXCALIDRAW flag.
apps/src/sketchlab/types.ts	Deletes Excalidraw-specific serialized state types.
apps/src/sketchlab/SketchlabView.tsx	Removes experiment branching; always renders React Flow Sketch Lab.
apps/src/sketchlab/reactFlow/utils/uploadBase64ToUrl.ts	Adds a new helper to upload base64 image data via POST/PUT.
apps/src/sketchlab/reactFlow/utils/convertExcalidrawSources.ts	Switches upload helper import; documents remaining @excalidraw dependency for migration.
apps/src/sketchlab/excalidraw/utils/uploadExternalFiles.ts	Deletes legacy Excalidraw external-file upload logic.
apps/src/sketchlab/excalidraw/utils/populateInitialExcalidrawState.ts	Deletes Excalidraw initial-state population logic.
apps/src/sketchlab/excalidraw/utils/index.ts	Deletes legacy Excalidraw utils barrel export.
apps/src/sketchlab/excalidraw/utils/imageUrlToBase64.ts	Deletes legacy Excalidraw image encoding helper.
apps/src/sketchlab/excalidraw/utils/handleSaveToBackpack.ts	Deletes legacy Excalidraw “save sketch to backpack” implementation.
apps/src/sketchlab/excalidraw/utils/generateNewExternalFiles.ts	Deletes legacy Excalidraw external-file metadata generation.
apps/src/sketchlab/excalidraw/styles/sketchlab-view.module.scss	Deletes Excalidraw view styling.
apps/src/sketchlab/excalidraw/introTour/useSketchlabTour.ts	Deletes Excalidraw-specific intro tour hook.
apps/src/sketchlab/excalidraw/ExcalidrawSketchLabView.tsx	Deletes the Excalidraw-based Sketch Lab view.
apps/src/sketchlab/constants.ts	Removes the legacy tour localStorage key constant.
apps/src/lab2/productTours/productToursPerLab.ts	Removes Excalidraw tour config and experiment-based availability gating.
apps/src/lab2/productTours/excalidrawSketchLabTourSteps.tsx	Deletes Excalidraw Sketch Lab tour steps.