use viewthatfits with scrollview fallback

[bretth18]

Description

This PR refactors the onboarding container view to improve layout flexibility and code organization, and updates the build version to v1.6.9. The onboarding content is now encapsulated in its own view, and layout adapts better to different content sizes and accessibility settings. Fixes #7.

Changes:

• Replaces the direct ZStack step switch in OnboardingContainerView with a new OnboardingStepContent subview, improving code organization and encapsulation. The step transition logic and animation are moved into this new view. [1] [2]
• Replaces fixed content area with ViewThatFits and a fallback ScrollView to better handle large content (e.g., large Dynamic Type or long localizations), improving accessibility and layout flexibility.
• Moves the animation modifier for the onboarding progress indicator to conditionally disable animation if "Reduce Motion" is enabled.
• Increases the onboarding container height from 520 to 600 to accommodate larger content.

How to test

• Ensure all checks pass

Author checklist

This PR:

• Satisfies a goal that is specific & clearly motivated
• Adds value in isolation (whether user-facing or sustainability-related)
• Contains a concise & easy-to-understand title + description
• Adheres to SRP by default
• Presents the best possible implementation to meet its goal, given constraints at hand