importing github project in offline app

[jwunderl]

fix microsoft/pxt-arcade#7515 (but more generally, fix importing github projects when in situations github view is disabled); when you load in project it'll work, just will have github information scrapped:

[Copilot]

Pull request overview

Enables importing GitHub-backed projects even when the GitHub editor UI is disabled (e.g., offline app / Electron), by proceeding with the import and stripping GitHub metadata before loading the project.

Changes:

• Removes the early “GitHub import not supported” guard and introduces a githubEnabled flag.
• Skips forced GitHub sign-in when GitHub UI is disabled.
• Attempts to scrub GitHub metadata from the imported header before loading.

[Copilot]

Clearing hd.githubId/githubTag/githubCurrent here is likely not enough to “scrap” GitHub info: during loadHeaderAsync, pkg.loadPkgAsync triggers workspace.recomputeHeaderFlagsAsync, which re-populates these fields from pxt.github.GIT_JSON (git.json) in the project files. This means the project may still be treated as a GitHub project (e.g., Save/Rename UI suppressed) even when githubEnabled is false. Consider removing the git.json file from the imported project (and persisting the updated header/files via workspace.saveAsync) when GitHub is disabled, or otherwise preventing recomputeHeaderFlagsAsync from rehydrating GitHub metadata for this import path.

Suggested change

	if (!githubEnabled) {
	hd.githubId = undefined;
	hd.githubTag = undefined;
	hd.githubCurrent = false;
	if (!githubEnabled) {
	// Scrub GitHub metadata from the header
	hd.githubId = undefined;
	hd.githubTag = undefined;
	hd.githubCurrent = false;
	// Also remove git.json from the project files so that
	// workspace.recomputeHeaderFlagsAsync cannot rehydrate
	// GitHub metadata from disk when the header is loaded.
	try {
	const files: pxt.workspace.ScriptText = await workspace.getTextAsync(hd.id);
	if (files && files[pxt.github.GIT_JSON]) {
	delete files[pxt.github.GIT_JSON];
	await workspace.saveAsync(hd, files);
	}
	} catch (err) {
	// Failing to scrub git.json should not prevent the project from loading.
	// Log the error for diagnostics and continue.
	console.error("Failed to remove git.json for imported GitHub project when GitHub is disabled", err);
	}