Update app icon

[austin-smith]

What Changed

• Updated the primary app icon from blue to teal.
• Preserved the previous blue artwork as a selectable alternate icon.
• Added the new pink artwork as a selectable alternate icon.
• Registered the blue and pink alternate icons in Debug and Release configurations.
• Added matching Blue and Pink previews to the app icon picker.
• Updated the documentation icon image.

Why

Refresh the primary app icon while keeping alternate color designs available to users who prefer them.

Validation

• Built the Debug scheme for a generic macOS destination.
• Built the Debug scheme for a generic iOS Simulator destination.
• Confirmed generated iPhone and iPad metadata contains the Blue, Pink, and Queen of Hearts alternate icons.
• Ran git diff --check.
• Ran structured review with no accepted or actionable findings.

UI Changes

The primary icon now uses a teal background. Blue and Pink variants are available from the app icon picker.

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