[ProjectInputStepView]: show "Cancel" instead of "Back" on first dialog step

[defymecobra]

Problem

The ProjectInputStepView component is used in two different contexts:

Context	File	Step Position	Back Action
OnboardingApp	OnboardingApp.cs	3rd step of 4	Navigates to previous step
AddProjectDialog	AddProjectDialog.cs	1st step of 3	Closes the dialog (CancelAndClose())

In AddProjectDialog, the view is the first step in the flow — there is no previous step to navigate back to. However, the button was hardcoded as "← Back", which is misleading. The onBack action actually calls CancelAndClose(), so the button should reflect that.

What needed to be done

The button label and icon needed to adapt to the context:

• When used as a middle/later step (e.g. in Onboarding) → show "← Back" with an arrow icon
• When used as the first step (e.g. in AddProjectDialog) → show "Cancel" without an arrow icon

What was changed

ProjectInputStepView.cs

• Added a new optional constructor parameter backButtonText (default: "Back") — following the existing pattern already used for skipButtonText and nextButtonText
• The button now uses backButtonText instead of the hardcoded "Back" string
• The arrow icon (Icons.ArrowLeft) is now conditionally rendered — it only appears when the button text is "Back", and is hidden for "Cancel" since a left arrow doesn't make sense for a cancel action

AddProjectDialog.cs

• Passed backButtonText: "Cancel" when constructing ProjectInputStepView at step 0

No changes to OnboardingApp.cs

The default value "Back" preserves the existing behavior — no modifications needed.

Result

Context	Before	After
AddProjectDialog (step 0)	← Back	Cancel
OnboardingApp (step 2)	← Back	← Back (unchanged)

[defymecobra]

Made the onBack parameter optional in ProjectInputStepView. When omitted (e.g. on the first step of AddProjectDialog), the back button is hidden since the dialog's close button already handles dismissal.

[artem-ivy-ai]

Staging removed

Staging environment has been deleted for this PR.