INC: Expose marp errors properly

[runxiyu]

In Sidekick/Logic/View Controllers/Tools/Slide Studio/SlideStudioViewController.c,

	/// Function to start `marp` preview server
	public func startPreview() {
		// Save the code
		self.saveMarkdownToFile()
		// Start the marp child process
		self.marpPreviewProcess = Process()
		self.marpPreviewProcess.executableURL = Bundle
			.main
			.resourceURL?
			.appendingPathComponent("marp")
		let arguments = [
			"--watch",
			self.markdownPreviewFileUrl.posixPath,
			"--output",
			self.markdownPreviewUrl.posixPath
		]
		self.marpPreviewProcess.arguments = arguments
		self.marpPreviewProcess.standardInput = FileHandle.nullDevice
		// To debug with server's output, comment these 2 lines to inherit stdout.
		self.marpPreviewProcess.standardOutput =  FileHandle.nullDevice
		self.marpPreviewProcess.standardError =  FileHandle.nullDevice
		// Run process
		do {
			try self.marpPreviewProcess.run()
		} catch {
			// Print error
			print("Error generating diagram: \(error)")
			// Return to first step
			Task.detached { @MainActor in
				Dialogs.showAlert(
					title: String(localized: "Error"),
					message: String(localized: "An error occurred while generating the slides.")
				)
				self.reset()
			}
		}
	}

The error handling code is a bit too generic, it'd be useful to tell the user what actually occurred. Perhaps read them to a buffer? (Obviously I don't know swift but it seems like people say you should create a pipe and asynchronously read from it to a buffer, which seems a bit cumbersome but w/e)

Also the formatting of the code here is a bit inconsistent (=, = ).

[runxiyu]

errr, .swift, not .c